new tips
I'm sure you'll need some room to do it, but have you thought about some ramps? They have some nice nylon plastic ones at walmart that are slightly shorter than the average ramps and they fit perfectly for the 996. They are so much easier to use than jacking.
As to the tips, the difficulty will depend on how much rust has accumulated on the clamp/bracket. How old is your car and where are you (in a rainy/snowy-salt-road area?). I recently changed the entire exhaust system on my car but re-used my tips and the bolts in the clamps were so rusted that I literally had to grind them off. I was able to re-use the brackets with new replacement bolts. If your bolts in the clamps are not that bad, try soaking them for a while in WD-40 or some other product (liquid wrench works well).
Good luck!
As to the tips, the difficulty will depend on how much rust has accumulated on the clamp/bracket. How old is your car and where are you (in a rainy/snowy-salt-road area?). I recently changed the entire exhaust system on my car but re-used my tips and the bolts in the clamps were so rusted that I literally had to grind them off. I was able to re-use the brackets with new replacement bolts. If your bolts in the clamps are not that bad, try soaking them for a while in WD-40 or some other product (liquid wrench works well).
Good luck!
If you haven't purchased your tips yet - I have OEM Factory Big Oval Tips in the classifieds section. These tips are easy to install. I've done it without a ramp/lift. It will be easier to reach up there with one though. The clamps will be sticky like Stevo said but WD-40 does do the trick. Make sure you align it right though before you tighten the bolts.

