Before you buy get a good understanding of how fast it writes. I've used SSDs that wrote so slow (mainly on cheap netbooks) they made the computing experience worthless. This Intel SSD is nice for the price: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5532358&CatId=4212
I put one in my netbook and it runs great.
If your looking to boost performance install the o/s on the SSD and keep all user files on HDD.
EDIT: whatever you do don't put the Windows Swap file on the SSD. It will be slow and can cause the SSD to wear before it's time.