What exactly does a telephoto lens do on a camera?

like this one= http://www.amazon.com/Opteka-Telephoto-FinePix-Digital-Camera/dp/B000TGVHS4/ref=sr_1_6?ie=UTF8&s=electronics&qid=1205174263&sr=8-6

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?

Is this a good lense for a beginning photographer?

I haven't actually started taking pictures but I already know I want a Nikon D3000. I really like pictures taken with a fisheye lens. Would this be a good lens for me to save up for so I can get it when I get my camera or should I take pictures for a little bit and then buy this lens?

http://www.amazon.com/Rokinon-Aspherical-Fisheye-Digital-Cameras/dp/B002LTWDSK/ref=sr_1_2?ie=UTF8&s=photo&qid=1257812086&sr=1-2

Sigma dSLR macro lens on a Nikon film SLR?

I currently have the Nikon N80 film SLR camera and was wondering if I could use a Sigma dSLR macro lens on it. This is the lens I'm looking at:
http://www.amazon.com/Sigma-50mm-Macro-Nikon-Cameras/dp/B0002P19Q2/ref=sr_1_4?ie=UTF8&s=electronics&qid=1241744118&sr=8-4

I know that this lens can be used with Nikon dSLRs, but I don't know if most dSLR lenses can be used on a SLR.

Thank you so much!