OK, not a bug or anything against eBoostr. I have used ATI 4650 and 4670 HyperMemory PCIe x16 2.0 cards (512MB and 1GB onboard, respectively) on a 6GB installed memory, 32-bit XP Pro SP3 test system to check on accessing and using unmanaged memory with eBoostr.
My Asus P5Q-E allows BIOS remapping above the 4GB limit for graphics cards. I suggest turning this off as eBoostr and any HyperMemory card seem to fight for that memory, the net result being ATI usually loses, and then in a dual-screen situation you end up without enough memory for your ATI card and it kicks your resolution down. I also enabled the 15MB Graphics Hole, but I'm thinking it more has to do with the memory remapping feature as I can reproduce the issue at will that way. My guess is this would not happen if you are just running a single monitor.
Again, not any problem with eBoostr. I need the HyperMemory cards for their low power draw. I'm not a gamer, but use my cards for business and Blu-Ray and such, otherwise I would just use a 2-slot version with enough memory onboard and/or a card with a 4 or 6 pin aux. power connector. I have an HTPC system using a 4670 2-slot solution. It is not a HyperMemory product and eBoostr has no issues accessing unmanaged memory on that system, which runs 32-bit Vista.