@ greymattr: Building your own can save a great deal of cash and although it's not really hard as such, can be daunting for the first time...Mine was, but then the first time is always a little frought😉
A complete new system may not be needed, though.
For example, is the case able to accept a new motherboard and PSU? If so you've saved 40-80 dollars there. Do you really need a new DVD/CD drive or hard drive/s? Again, by reusing more can be saved there. Need the OS? Get the 'system builders' version, it's the same product but a fraction of the retail price. Will you overclock? No? Then there's no need for a high performance CPU cooler. Memory should be bought, though, most likely yours is a slower type and will hold a faster CPU back, particularly the newer AMD chips.
Such a core upgrade could be done for about $250-$300 (CPU/MB/RAM/PSU and a HD4670 or HD4870 card.