Fixed the issue for me with an old Dell Vostro laptop. Took out the additional 1Gb memory stick and the SCCM OS deployment went through fine (though a bit slow with just 1Gb total RAM! 🙂
Let the install finish and plugged in a new memory module. All good. Chucked the old one in the bin as although the OS may look like it’s working, I don’t want the user coming back to me in a few days or months with blue screen or lockup issues.