First of all, export all the data from Outlook into PST files. Then get those off the harddrive, for instance by placing them on a CD-RW or DVD-RW. Also export your sorting rules if you have those, and your contacts. Once that is done, you'll be able to recover if things go south.
I would strongly urge you to do the same with any and all documents you have. Nothing beats backups when doing any sort of work on the machine.
Frankly, if I were you I'd be cranky about the apparently shoddy work the repair guy did. I'd also consider going the backup everything-format the machine-start from scratch route, but that may be too over the top for you.
If reformatting is too much then I'd at the very least do "backup Outlook and everything else, remove all Office installs and reinstall 2003" - but that's just me.
There are lots of info resources on the web on how to backup Outlook. Here is the first one I spotted when I googled - it should be fine but don't blame me if it isn't.
http://www.sitedeveloper.ws/tutorials/outlook.htm
