Here're a few ideas for developing a trouble-shooting strategy to solve your problem. Of course, you'll have to adapt these methods to you're specific situation and discard the ideas that don't apply. First, I agree with Larry that it's very unlikely this problem is related to your Maxtor HD.
A) Checking for resource conflicts in WIN2K:
It's normal for WIN2K to assign a lot of devices to one IRQ number, usually IRQ 9. Resource conflicts are rare in WIN2K, but they're usually very easy to spot. Log in as an Administrator.
1) CHECK YOUR EVENT LOGS: click Start > Settings > Control Panel > Administrative Tools > Computer Management. On the "TREE" window (left) expand System Tools, then expand Event Viewer. Click on the System icon and look for error messages -- circles with a red X. Look in the Source column and see if either of your network cards is listed. If so, right-click on the error line to get a detailed description of the problem and an event number for trouble-shooting.
Also, in the Event Viewer section, click on the Application icon and see it there are any errors associated with web browsers or FTP applications (assuming you're using ethernet TCP/IP).
2) CHECK DEVICE MANAGER: click Start > Settings > Control Panel > System. Click on the Hardware tab, then click on Device Manager and expand the Network Adapters section. Click on each adapter listed and click on the Resources tab. Check the Conflicting Devices list (bottom) and make sure it says "No Conflicts". If you see "No Conflicts" for each network card, you can be virtually certain that you're problem is not related to a WIN2K resource conflict.
B) Checking for "Flow Control" errors and bottlenecks:
From the symptoms you describe, it's possible you're having "flow control" errors and bottlenecks. Depending on the features of your particular NIC, you may have more or less control over your hardware flow control settings. Before you play with your NIC flow control settings, it's usually a good idea to monitor your network interface for awhile to get a baseline view of performance during high-speed downloads.
1) MONITOR YOUR NETWORK INTERFACE: click Start > Settings > Control Panel > Administrative Tools > Performance. In the "TREE" window (left) click on the System Monitor icon. (I assume the System Monitor snap-in has been installed by default. If not, you must install it before continuing.) In the Details window (right-hand panel) Right-click to open a small dialogue box and choose Add Counters...
In the Add Counters dialogue box, open the drop-down menu labeled Performance 0bject. By default it will be set to Processor. Change it from Processor to Network Interface. In the right side of the dialogue box select which ever NIC you need to monitor during a high-speed down load. You have several choices to monitor. I would start out with Packets Received Errors, Packets Received Discarded and Packets Received/sec. Do an appropriate monitoring program for each NIC during a down load to check performance. Create a log you can refer to later.
2) MONITOR YOUR TCP CONNECTION: Once you've monitored the Network Interface, go back to the Add Counters dialogue box and change the Performance Object from Network Interface to TCP. Under TCP you can choose to monitor such items as Connection Failures, Connections Active, Connections Passive, and Segments Received/sec. Again, create a log during the download you can refer to later.
You could also monitor your RAM, but it's probably not related to your download stalls.
3) ADJUST YOUR NIC "FLOW CONTROL" (if possible)
Click Start > Control Panel > System. Click on Hardware tab, Device Manager button, expand Network Adapters, and select your adapter. Click on the Advanced tab and look for the item in the left window that says "Link speed/Duplex Mode". The dropdown menu on the right, labeled "value" will probably be set to Auto. You may have to adjust the settings in this menu to conform with your network. This depends on whether your network is half duplex or full duplex, and how much bit density your NIC can handle. In most situations the Auto setting works best because it can usually adjust for network speed and duplex configurations. But it's worth a look.
You may also want to experiment with lowering your Early Tx Threshold value, also found on the NIC Advanced tab (if supported). Use the Monitoring functions above to see if you can produce any improvemet. Remember to write down your original Tx Threshold value so you can reset it if necessary. Adjusting Tx Threshold is unlikely to resolve your problem, but it's worth a try.
C) Simplify your hardware configuration:
You state that your problems may have started when you installed a second NIC card. There may be a reason for running two NIC cards at the same time, but if possible I would think through your situation and see if you can make all of your network connections using only one.
You may NEED two NICs, if you are connecting to two incompatible network stacks, or if you are using your PC as a Bridge/Router between incompatible network segments. If this is not the case, then you are probably better off using only one NIC.
D) Check for mutual NIC interferece problems:
1) Let's suppose you NEED to run two NICs for reasons I don't understand. Then you may want to see if they're interferring with each other. The easiest way to do this is to go into the Device Manager and temporarily disable one of the NICs. Then do a high-speed download with the other NIC and see if you still get a lock-up. This strategy will at least help isolate the problem. If the NICs won't work together, maybe one of them will work independently.
2) If you find that one NIC works independently, another possible solution is to create a separate hardware profile where only one NIC has it's drivers loaded. Then you can use that profile for high-speed down loads, and use to your normal hardware profile for all other PC functions.
I hope this will give you some ideas on how to develop your own best strategy.