On this page: http://www.terry-is.f2s.com/ i fond this picture: http://www.terry-is.f2s.com/future/linbearing/linearb.html
is there anyone who uses this design with beltdrives?
It looks useble :)

Yep, I use a variation of this. I have THK linear guides with a belt drive like this. Works good!

No problem with backlash??

looking at it, with it properly setup and maintained, you'd have to think that there's less backlash than using lead screws. May want to add a tensioner pulley so that it can maintain accuracy as the belt stretches over time.

Timing belts are seeming more appealing to me... the following page has a spiel... http://www.torchmate.com/motors/electronics_selection.htm

...the bottom of the bage has a quote:

"In our view, the only satisfactory type of moderate-cost drive system uses powerful stepper motors in conjunction with a timing belt/pulley reduction without backlash. We have tried them all"