Jim,
Unfortunately for you Nikon changed their flash system from DTTL ( very clever ) to iTTL ( near foolproof ) in the interval between the D100 and D200. That means that flashguns compatable with iTTL are all fairly recent.
When you start using flash other than the pop-up, you really need the foolproof option that iTTL will give you. Probably an important feature for your style anyway.
Once you get going you will get more creative with your lighting, and that is where a good selection of manual power settings becomes important.
So whatever kit you buy consider it as a long term purchase. Better to save up and get a unit that will satisy you for years, than get something you will quickly outgrow. If you have to sell an under featured unit once you grow out of it you will loose £££.
As I mentioned Metz is a known top brand and I would happily recommend it to anyone. Spent some time on a net dealer rummage and used SB-600's seem to be around £170 mark and Warehouse Express are doing the Metz 48 AF-1 Nikon for £175. So the Metz gets my vote.
Not at all sure I would consider an e-bay job. They are not the sort of thing you can easily take a screwdriver and soldering iron to if they have a fault.
Regards to Gabby. I will now have to do a net search for info on the Yashica before he blinds me with science.
Don