My first question to you is what kind of RAM does your P4 support? Some Motherboards support PC-100/133 SDRAM with the P4 and others may allow DDR or Rambus. If you're using SDRAM with a P4 it's almost pointless because the RAM chokes the life out of the processor. This most likely would not be the reason for your PC acting sluggish but it does play a factor.
Another question might be the software you're running on your computer. Are you using a software firewall or AntiVirus software? These tend to take up alot of resources when they are being used. Have you installed any freeware software lately?
Have you ran a virus scan lately? When I work on client computers I usually run an antivirus scan online at
http://security.symantec.com/ssc/lu...ie&venid=sym&plfid=23&pkj=VQPJXIBVEMBQAUWZKTK
There is also a chance of you having a corrupted file system. Are you running FAT32 or NTFS? Open a command prompt and type
chkdsk /f /r to scan your HDDs, you will have to run it on all of your hard drives (e.g. C:, D

. chkdsk or checkdisk will scan your HDDs for errors and problems. The /f switch will fix any errors and the /r switch will report any bad sectors etc.
I recommend cleaning your computer up, defragging (preferrably speeddisk or diskkeepr) and running a virus scan. Hope this may help you.