Mountain Biking - Will these derailluers mount to my bike.

I have a 96 steel frame Gary Fisher, that I want to build up. It has the org derailluers on it now and there pretty fried. I want to put a Deore on the back and im thinking this one on the front if it will work on the steel frame.
http://www.jensonusa.com/store/product/FD707A02-Shimano+Xt+Fd-M750+Front+Derailleur.aspx

Any help ASAP would be Awsome, for I would like to order by the morning, they are running some great deals right now and discounted shipping.

Measure your seat tube diam.

Not too likely a 34.9 will fit on an older steel frame...

Ok, so can I still find new ones that will?

Ok, so can I still find new ones that will?

As Ed pointed out, you need to measure the seat tube diameter, that's what the front derailleur mounts on. A lot of front derailleurs will come with shims that allow you to mount on any of the three common tube diameters. Some are sized for just one diameter, like the Jenson one in your link.

You also need to consider whether the front derailleur is top pull or bottom pull- meaning the cable will come either from below (bottom pull) or above (top pull) to the derailleur. Again, some derailleurs are universal, and can do both top and bottom pull. Check the listed specs. on the particular model you are looking at.

The Deore rear derailleur will be just fine.

You also might run in to trouble switching from a top swing clamp type to a bottom swing...or the other way around. (the water bottle cage boss might be in the way of the clamp)

Cool, thanks for the info, that helps alot. I did find on Bike Pedia that is says the seatpost is a 27.0mm. So that is the size I need to be looking for?

Cool, thanks for the info, that helps alot. I did find on Bike Pedia that is says the seatpost is a 27.0mm. So that is the size I need to be looking for?

I should have pointed out that a shim would work with that fd, but from memory the M750 didn't come with one (and the ad doesn't say one way or the other).

The seatpost measurement is the inner diameter of the seat tube, you need the outer diameter measurement. I'd guess it's a 28.6, but that's a guess as you don't specify the particular bike. Like the others said about top or bottom pull and swing (the one in the ad is a top pull, and I'd also guess the Fisher is a top pull).