why my pc runs slowly

In windows 2000 hit ctrl-alt-del and go to task manager. Look for a task thats hogging your cpu time and kill it. You may need to look at your startup programs and remove some. Also check for spyware, worms and virus. If you are using an internet file sharing program like Kazza, your in trouble

The first answer is right on. Look for free spy\ad-ware removers. The two best are AdAware by Lavasoft and SpyBot Search & Destroy. I use both with much sucess!

http://www.docsdownloads.com/spybot.htm

http://www.lavasoft.de/

Remove any spaces from the pasted links!

Those two are excellent and I use them all the time. In addition, you might need to purchase something like Spy Sweeper from www.webroot.com and Pest Patrol at: http://pestpatrol.com/

W2k doesn't come with msconfig, but you can use one from windows 98 or ME to see what is in the startup, uncheck anything unneccessary and reboot. I use it on my w2k at home, not sure which one it is. Big oversight by M$.
Also look in Systems for IRQ conflicts and Forced hardware.
Video card is important when doing photo work, you didn't mention your card. Make sure you have latest drivers and a card with at least 32MB, preferably more.

Above answers are grea, but have you looked at the anti-virus configuration ? Heuristic (probably mis-spelled) virus checker will slow it down greatly when checking a large file. Photo shop to start with is slow to load, anti-virus will almost stop it, and of course the larger the file the slower to load. 1200 DPI can be a 20-75 Meg file, talk about slow while loading/anti-virus scanning !

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