An upgrade is possible, but your only upgrade path is really the X2 4400+, which doubles the L2 cache size and nothing more. You can find it for $30 at http://www.ebay.com/itm/Genuine-OEM-AMD-Athlon-64-X2-ADV4400DAA6CD-CPU-Dual-Core-2-20GHz-Processor-/281444649334?pt=CPUs&hash=item4187688976, but the performance benefit will be very slim.