My ex was having the same problem with her Dell with Vista Home Premium and I ran across a question to Ask Neil in the May 2008 edition of PC Magazine
http://www.pcmag.com I performed this action on here machine and it worked great, Neil says it may not work on every machine but it worked on hers. This solution fixes an issue between Vista's "Auto Tuning" and some routers and network devices. Here is the procedure, I am posting it exactly as it is in the magazine so you can cut and paste.
At the Start menu type
command, but don't immediately launch the command prompt. Instead right-click it and choose
Run As Administrator Now type this command;
netsh interface tcp show global
If the line
Receive Window Auto-Tuning Level does not say "disabled", enter this command
netsh interface tcp set global
autotuning=restricted
Better? If no change repeat the above process but use the command
netsh interface tcp set global
autotuning=disabled
If this didn't help you might as well put things back to normal by repeating the above but finishing with the command
netsh interface tcp set global
autotuning=normal
I copied the above verbatim from the magazine. I am adding this, after making the change reboot the machine and see if it's better, the magazine didn't say anything about rebooting but I didn't see any improvement on her machine until I rebooted. I've gotten into the habit of rebooting after I make changes just to be certain I am actually working with the new settings. I hope this helps, good luck.