2 gig is not a lot now days and it would likely do a little better with more memory, but I would be surprised if this is your problem.
If you open task manager in windows and check under the Performance tab, it will tell you how much memory you are using. Likely about 1G.
Which DIMM slots are filled?
Do you have 1 or 2 processors?
Are you running a 32 bit or 64 bit OS?
What BIOS level are you using? (Press F2 during POST and you can read it in the BIOS set-up window.)
Are your drivers current? Especially the network drivers since it sounds more like a network issue than a memory issue.
For best memory speed, fill the blue slots first then black
if you want fastest, only use the blue slots and go to 1G or higher dimms.
if your running a 32 bit OS, no point going past 4g total, so I would just get 4 more DIMMs like the ones you have now and add them into the black slots.(Fewer issues if the dimms are matched)
or just replace them with 4 - 1G dimms.