Would anybody know of anywhere that could convert a poptop camper into a rag top style sliding roof??.........does anyone know how to go about this??....cheers.

yep can do....
theres a guy at newcastle (karstan)who has just installed one him self.
he said its pretty easy to do, wont leak unless you high pressure was you car an shoot water up undeneath, but only a small amount.
Hasnt had it leak with the weather weave had and was up at old bar last weekend ,pooring down ,an no leaks which shows there qaulity.
cost about $1100 delivered from the u.k.
Here the link for you.....
http://www.parisbeetles.co.uk/bus%20sunroofs.htm 

Thanks mate..........thats the go i think.

If you want to send me your email address I will send you the installation instructions. They are handy to have as you need to cut your roof out a bit to make sure it is 100% square before making the order.

can you do this to tin top roofs? as in no camper at all, and just cut a hole and wack in a rag top into the top of a kombi?

does it mess around with the strength and structure of the vehicle?

You sure can. The purists would say don;t cut a good roof, and I cannot bring myself to sut my roof to install the 2m sunroof I have sitting at home, but if you do it you have to sure up the hole.
For a 2m long one like what I was going to put in, you would use the front supprt where it is, the middle one you would shift to the back and the long sides of the hole would have to be supported with 25x25x3mm angle. (or you could bend up a similar section to the cross supports so it looks factory.)

Otherwise, if done right it is no different to having a pop top. Probably should get an engineers certificate I suppose though.