swap IDE hard drive with another IDE hard drive

Hi guys, I have a IDE hard drive on my windows xp system which is almost full...and I have another IDE hard drive that I use as an external hard drive via a 3.5 IDE HD encloser with USB connection...Is it possible to just switch hard drives after I do the necessary manual copies of the Documents & Settings folder and programs folder..to disconnect the old one and connect the external one as the internal one..both same physical size although the old one only has 100 gig and the one I want to swamp in is at 300 Gig

Please advise

Thanks