it's possible, i have done it before. i forget how i did it though. i think it was either in my BIOS, or you can edit boot.ini and msconfig. i'm not sure though wait for someone who knows for sure before you do anything.
Acer Aspire 5102WMLi
Windows Vista Ultimate x64
AMD Turion 64 x2 TL50 (1.6 GHz, 512KB L2 cache)
ATI Radeon Xpress 1100
120GB 4200rpm PATA HDD
1GB DDR2 (support dual-channel)