Using Beta 4.0 Build 544 in XP Pro SP3.
Installed 2x2 GB RAM, in addition to existing 2x1 GB RAM, for a total of 6141 MB (same brand, speed, timings). eBoostr reports *8184* MB available of 6141 MB total. However, it also reports 2559 MB unmanaged, which is accurate, and it seems to be using this memory without any issue (gets a 58.5 ratio).