Upgrade from XP Home to XP Pro

I have a (new to me) client with a p2p network — W2K server, 1 XP Pro, 2 W95, 1 W98, and 4 XP Home machines. I want to upgrade the XP Home machines to XP Pro so that I can create a domain with the W2K server. Customer has several complex programsrunning on these machines. Is it safe to do a write-over upgrade from Home to Pro, or would I have to do a fresh install?