Comment From the IT department's perspective (Score 1) 475
Talk to your IT department, say "my computer runs slowly", and see what they say. I'm serious, keep it simple and to the point. Say what the problem is, not the solution.
They may well have more RAM around lying spare, 1GB is about the minimum for Windows XP SP3 for a comfortable experience without too many heavyweight apps running, 2GB for Vista. I haven't tried Windows 7 with less than 2GB, but it's touted as running faster than Vista in the interest of netbooks etc.
Use Window's performance mode instead of "let windows choose" (right click on my computer > properties > advanced settings). You may want to tick a few extra options if you notice fonts are too jagged or you want to view pictures as thumbnails in windows explorer, etc, etc. Use Smooth Screen Fonts and Turn On Drop Shadows are the only two I normally bother with
Setting your swap space to a constant size, about 1.5x your RAM, tends to make the system run slightly faster. ie. set the minimum the same number as the maximum instead of "let windows choose".
If your hard drive needs defragging, do it.
Without knowing what kind of company you're in, you may find your IT department don't support browsers other than their standard IE6 / IE7 / whatever. So the internal web applications and intranet might not behave quite as you expect.
(I've worked in various IT support roles for the last 5 years including a lot of desktop support)