With Windows 7 being released this Thursday (October 22), I should be getting it from Acer whenever I order it (free because of the Windows 7 Upgrade Option but I was wondering:

As my laptop has 3GB of RAM, should I install the 32-Bit or 64-Bit version of Windows 7?

Go for 64-bit, unless you have a specific reason not to (incompatible hardware or software, for example).

64 bit all the way! If you got a 64 bit system but a 32 bit OS prepare to hate your compie! I had xpsp3x32 on my 64 bit PC and I would often have bluescreens, applications not loading all the way (ie 60% of the interface), Photoshop would only load half of its interface. If I would have too many (20) browser tabs open I could not open any other applications. If I had PS open, 5 browser tabs, mediaplayer11, and two explorer windows, opening the third explorer window was not possible. Also if you use PS on a 32 bit OS/64 bit hardware, your scratch disk would run out in 30 minutes or less (working with 1600x1200 images with 6 layers and 30 actions -my normal retouching setup) This would require closing an reopening of photoshop witch takes approx 3-8 minutes with a fullbrushes file (120MB) and 20 patterns and 50 gradients loaded--After just ONE picture!