This may be a little long, so thank you in advance...I'm currently running XP SP2 with a gig of RAM (Patriot Extreme, 1 stick), and an E6400, on an Asus P5B Deluxe...over the last 6 months, I've experienced extremely strange behavior from my computer. After some time (even if the computer is just idling), XP acts like it's running extremely low on memory resources (even though it doesn't provide any warnings). I can't open multiple programs, or even individual folders including My Computer and My Documents (at least without trying to end a number of processes first, and often they appear messed up). If I try to open Zoom player, it'll show up as a black box (as opposed to the normal GUI), and is often accompanied by a continuous hard "ding" sound (warning tone used by Windows); the continuous dinging also happens if I try to open other programs or folders as well. If I can open Firefox in this state, it won't open more than a few tabs before it refuses to display the webpages on any new tab I try to open.
In addition, after closing a window, the destop icons blocked by the window take a long time to reappear...and if I try switching users (so that I can log off without closing my running programs) and then log back in, the desktop icons are somewhat "messed up" for about a minute--the bottom line appearing below the taskbar--before returning to normal.
This state usually occurs more quickly if I use memory intensive programs like Azureus, or if I leave Firefox open for a while. I've checked the task manager for signs of a memory leak, but neither the physical nor virtual memory usage seems extraordinarily ridiculous. Even after I close the biggest memory hog running, I still get this slow, incredibly-frustrating performance out of my machine. I really have no idea what's going on, and I actually reformatted and reinstalled about 4 months ago trying to resolve the issue. It worked fine for a month or two, but it came back...is it a virus? A corrupt Windows file? A driver? RAM? Motherboard? I don't know, but if anyone could help, I would be incredibly grateful.
Try to see if you have any spyware, those could be resource hogs.
Also you can try to disable some services.
One of the services I always disable is Indexing.
By turning off services you will free some MBs of RAM.
Another service you can turn off safely is Themes but your XP will look like Windows 2000!