naw....cpu's aren't hard to take out at all! you can buy a motherboard with the same socket and just transfer the cpu and your ram, just make sure it supports the type of ram and is the same socket as your cpu and you'll be all set. I don't know of anything that would fit in a dimension 3000 case that you can buy off the street, you'll have to buy one from dell. therefore you might want to buy a new case to go with everything. you said you only have 3 pci slots so it sounds like you have a micro-atx motherboard, if you buy a new case, you can install a regular atx motherboard and have more pci/pci-e slots to work with.
if you have windows xp and you upgrade your motherboard, you would have to reinstall windows, you can use the same hard drive though.
so basically, a lot of your parts are transferrable to a new motherboard like the cpu, ram, hard drive and optical drives and you'll want to buy a new video card which will be just fine, and if you buy a motherboard with pci-e slots you can get a really good card.
