Update: $90 headset press saved my frame, and I'm done listening to the 'just use a block of wood' crowd
Everyone keeps saying you can seat headset cups with a wooden block and a hammer, but I tried that on a customer's steel touring frame in my garage in Pittsburgh two weeks ago and it went in crooked and chewed up the cup edge. I bought a proper Park Tool press for around $90 after that and the next three frames went in dead straight in under a minute each. I'm not saying you need the fanciest gear, but that cheap trick cost me a $40 replacement cup plus an hour of sanding and swearing. Anyone here actually had good luck with the homemade route, or did it bite you too?
The wood block trick only sort of works if the block is perfectly square and you whack it dead center, which nobody actually does. What most people miss is that you can rent or borrow a press from a local shop for basically nothing, or a lot of co-ops in bigger cities have one on the bench you can walk in and use. I've also seen guys make a DIY press with a threaded rod, two big washers and a nut for like $12 at Home Depot, and that gets you the straight pull you need without the hammer guessing game. The crooked cup is really a tooling problem, not a skill problem, so the fix is just getting something that pulls evenly instead of pounding.