I just completed 10 cycles of the memory test after upgrading to 4GB with the Kingston KVR800D2K2/4GR (2x2GB). Testing took about 13 hours and there were no errors. These DIMMs are in stock at both Frys and NewEgg.
FrontView now reports
4096 MB [6-6-6-18 DDR2]
The bracketed numbers are unchanged from the stock 1GB DIMM.