Mike, I would recommend to get some good sturdy brazed-on eyelets on your bike. This can be easily done at your local bike shop or mechanics especially if you have a steel frame. Otherwise there is another option to mount your rear rack without eyelets using a couple of the Tubus accessories. Tubus make the a QR-axle mounting adapter to attach the bottom of the rack, and they also make a "clampset" for attaching the top part of the carrier to the seatstays. A friend of mine who has an aluminum frame choose that option and he is quite happy with it (although he travels quite light). I don't see the clampset on cyclocamping.com but I know they were able to get it for my friend so perhaps Stephane can help you with that.

Here are the Tubus instructions for the clampset (it's pretty straightforward but you'll need to know the diameter of your seatstays): http://tubus.com/images/stories/articleimage/download/montageschellenset.pdf
Ane here is the link to the QR-axle adapter @ cyclocamping.com: http://www.cyclocamping.com/proddetail.asp?prod=GOT71500

But again I would try to have some brazed-on eyelets if I were you. The load capacity is much higher with eyelets. I would not carry more than 40-45 Lb with the adapter and clampset system, and even less on bad roads.

Good luck.