I can't seem to fullscreen when windows aero is disabled

I run a pretty old laptop, and I've been noticing performance issues in Minecraft (which I mainly play on it), and so I decided to disable some visual features. I noticed an instant performance boost, but for some reason I can't fullscreen when windows Aero is disabled, which is a pain as Aero takes up quite a few resources. Please help!

Specs

OS: Vista Home premium

Ram 2gig

Ghz:1.7

Screen Res. 1280x720

Processor Intel® Core™2 CPU T5300 (dual core)

32 bit OS

And it is the Acer 5310

Also, if you can think of any other ways to improve performance, that would be great. (that don't involve buying new parts)

via Bleeping Computer Last 20 Posts http://www.bleepingcomputer.com/forums/t/510809/i-cant-seem-to-fullscreen-when-windows-aero-is-disabled/