I am buying a new 80gb hard drive to replace my 20gb. I have partition magic on the 20gb drive and i plan to set up the 80 gig on a seperate ide cable and then use partition magic to copy all my partitions. Is this the best way to do it? How long will the copying of 20gbs take?

Are you using NTFS Partitions? If so, yeah, copying the 20GB partition isnt a bad way to go,
i suggesst you create a seperate partition for your Page File, as it is faster, and if your keeping your 20GB HDD in the computer, put your page file on that drive.

I would just burn your data to CD, and reinstall everything on the new drive, everything will run better.

The transfer shouldnt take long, HDDs are very fast for data transfer. It might take an hour or two, its gonna be slower than normal, because its going to copy it Byte for Byte.

Disk to Disk is the way to travel.

How long, it is a combination of file size/ memory size / disk read/ disk write/ bus speed/ CPU speed.

However a FULL 20GB will be finished by the time you wake up: so start the process off and go to sleep, watch a movie or some useful activity.