I just switched from XP Pro 64 bit back to XP 32bit...Okay I know that 32bit will only use 2GB of Ram....will it make my computer run slower if I just leave all 4 in or do I remove the other 2 sticks? ...

No. Leave them. 32 bit can use up to 4GB. Some will go to hardware but you should get usage of more than 2GB. Leave it in.

You could also start running Windows 7 RC1 if you wish for free (trial). It recognizes 4GB but again will show you some is tied up in hardware.

Thanks Jephree!

I just reloaded XP 32 on my upgrade with 4GB RAM and XP is using 3.33GB.

It's normal that the 32bit system recognized the RAM less than 4 GB, only 64bit system can use the RAM more effectively.

Hope this helps!
Bill