Are SLR and DSLR lenses interchangable?

I have a Canon Rebel G (SLR) and was wanting to make the switch to a DSLR, but was wondering if the lenses from my Canon SLR would also work on a Canon DSLR (which would save me a couple hundred bucks).

Any thoughts?

Are these lenses any good? (for 35mm camera)

I'm looking for a wide-angle lens and a fish-eye lens of some sort for a Canon Rebel G. I'm not sure if they make real lenses for this thing or if this is just how they are for older cameras.

Are any of these decent?

http://cgi.ebay.com/pro-fisheye-lens-fits-canon-rebel-g-gii-2000-eos-slr_W0QQitemZ110276967851QQcmdZViewItemQQssPageNameZRSS:B:SRCH:US:101#ebayphotohosting
http://www.amazon.com/Opteka-Angle-Panoramic-Macro-Fisheye/dp/B000HVD8D8/ref=sr_1_4?ie=UTF8&s=photo&qid=1218500446&sr=1-4
http://cgi.ebay.com/WIDE-ANGLE-LENS-For-CANON-EOS-Rebel-2000-ti-G-GII-K-K2_W0QQitemZ130245392195QQihZ003QQcategoryZ3323QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Are there any better options out there for this camera?

lenses used on camera usable on digital also?

I have a canon rebel g 35 mm camera and was wondering if the zoom lens, etc. would be compatible with a digital camera also? I planned to sell the entire set then realized I may be able to use the zoom, etc. on a new digital camera and therefore should not sell!
anyone know for sure?