That fancy board has 8 slots.
Read the manual closely to figure out the best slots to choose.
quote:
# Single or Dual (recommended) channel memory support
# For Single CPU: Memory must be populated in CPU1 DIMMs only
# For Dual CPUs: Recommended that memory be populated equally in adjacent memory banks
If you already have 2 x 1gb, and you have dual CPU's, I would buy another 2 x 1gb and have dual channel setup in each set of slots.
Not that obtaining registered ECC DDR400 will likely be more expensive than newer memory tech. If the board can deal with non-ECC (and your existing memory if re-using is non-ECC) that would make it easier.