The following tip will help ADSL/Cable Modem users to increase their broadband connection speed in Windows XP 
The broadband connection tweaking process incorporates the enabling of a special buffer in the computer's memory to better deal with Networkd Interface Cards (NIC) or the USB modem.
I recommend this tweak to users having 256 MB RAM or above due to some technical reasons.
Step #1 - Identify the IRQ used by the NIC/USB modem:
Follow these steps:
1. Open the System Information tool by running MSINFO32.EXE from the Run command.
2. Expand System Summary > Hardware Resources > IRQs.
3. Look for the listing made for your Network Interface Card (NIC) and note the IRQ next to the specified line.
In case of USB modems you will first need to find the right USB device used by your modem. Follow these steps:
1. Open the Device Manager tool by running DEVMGMT.MSC from the Run command.
2. Scroll down to Universal Serial Bus controllers and expand it.
3. Right-click the USB Root Hub and select Properties. Note that you might need to do so for all listed USB Root Hubs (If there are more than one) in order to find the right one.
4. In the Power tab, look for your USB ADSL modem.
5. In the Resources tab, look for the assigned IRQ.
6. This is the IRQ we are looking for
Step #2 - Modify the system.ini file
Follow these steps:
1. Run SYSEDIT.EXE from the Run command.
2. Expand the system.ini file window.
3. Scroll down almost to the end of the file till you find a line called [386enh].
4. Press Enter to make one blank line, and in that line type
IrqX=4096
where X is the designated IRQ number we found in Step #1.
5. Click on the file menu, then choose save.
6. Close SYSEDIT and reboot your computer.
Done 
After the computer reboot you will notice Speed Improvement 
. If this hack works for you I would love a word of admiration