I know I need a new belt.  It squeals every time I start it, then it quickly goes away, like in a couple seconds.

When I got the thing, it came with a can of belt dressing in the glove box, so obviously the problem was pre-existing, and I'm assuming the previous owner used the belt dressing frequently.   

Here's my question.  What should I do, if anything, to the pulleys when I install the new belt?

I would look at:

Crank Pulley - for wear
Alt. Pulley - for wear
Bracket & alignment
Verify the belt

These items are 24 years old and are used / abused each time the vehicle was started. Pulley's do wear to the point of replacement. Bracket alignment could be off causing the belt not to ride correctly. The bracket itself may not be the correct one. Having had possibly several owners it is hard to determine sometimes the items previous owners have changed modified. I would also verify that you have the correct belt numbers for you application. again just because it is on the vehicle doesn't mean it is correct.

Loosen it up and check all the bolts on the alternator and adjustment arm. I have had one or all the bolts come loose and even lost some. I have also had the adjustment arm break. And once I had the bracket that bolts onto the block and the alternator bolts to break. If it is squealing, there is a problem period.