If you have cash
Get a dual xeon board (super micro, asus have a few that supports socket 771)
Get an e5405. or a pair.
Get more RAM like 8G.
HD, you can do some RAID 0/1/5. Raid 5 need 3 drives. RAID0 or RAID1 uses 2 drives.
Research on solid state drives as well (they are great for speed / low...