Bicycle Mechanics - Can I use a triple shifter with a double crank?

I'm converting my old Fuji from downtube shifting to STI, and my friend is going to give me his old Sora brifters. Here's my question: the front shifter is for a triple ring, and I have a double. By setting the limit on my front derailleur, will this alleviate the problem of the third shift? Also, the Sora rear shifter is an 8 speed, but I have a 7 speed freewheel on the rear. Can I do the same thing and set the limit so the shifter can't shift into the 8th slot? I've been told that 7 and 8 speed cassettes have the same spacing, but I could be wrong...

I'm converting my old Fuji from downtube shifting to STI, and my friend is going to give me his old Sora brifters. Here's my question: the front shifter is for a triple ring, and I have a double. By setting the limit on my front derailleur, will this alleviate the problem of the third shift? Also, the Sora rear shifter is an 8 speed, but I have a 7 speed freewheel on the rear. Can I do the same thing and set the limit so the shifter can't shift into the 8th slot? I've been told that 7 and 8 speed cassettes have the same spacing, but I could be wrong...

The double with a triple shifter is not a problem for the reasons you specified. Some people with mad skills can set up the triple to work as a 'trim' adjust... YMMV on that one.

Some people just cannot live with the shifting quality of an 8 speed shifter with a 7 speed cluster... The spacing is slightly different. It will be more tempermental and you may or may not find it acceptable.

If all else fails a halfway decent cassette wheel isn't too expensive and do have their advantages...

I have a triple shifter working with my double crank. I set it up, like TO11MTM said, with lots of extra trim adjustments. I can now get to any rear cog from the either front ring without any kind of rub whatsoever. Its quite nice.

There may be a differance between shifters though, I use 105 Brifters, they might be a bit differant than Sora. Im not sure there.

About the 7-8 speed compatibility. You could always throw on a new cassette and call it a day.

-Jerry

Well, the bike came with campy wheelset that I like, and it uses freewheel cassettes. But then again, I also have a wheelset laying around that has a freehub. I may just sell the old campy wheels, to cover the cost of the $75 I paid for the whole entire bike. Then it'd be like having a free bike, because I'd definately pull more than $75 for these wheels.

An 8-speed cassette won't fit on a 7-speed hub.

If you set up the shifters with the 7speed freewheel I'd like to hear how it turns out. What kind of freehweel is it?

It's a Sachs freewheel on a Campy Super Record hub. It's funny, because this is the only old steel frame I've messed around with that actually has 130mm spacing. I'm seriously considering saving up to buy someone's used Ultegra 9 speed group and really modernize this thing.