You frame is spaced 126 mm and 8-speed anything requires 130 mm so you will have to "spring" the frame to get a new wheel in. You can either struggle a bit each time or have the frame "cold set" (permanantly reset) to make it easy. And yes, your Maillard hub won't accept any of the newer cassettes.
BTW "STI" and "Hyperglide" are Shimano trade names. Campy calls their brifters "Ergo". The two makes' hubs and cassettes won't interchange either.
Unless you already have 8-speed brifters, don't bother with 8 and go all the way to 9 or 10. Eight speed is obsolete and both Shimano and, particularly Campy, 8-speed components are getting hard to find.
This could be a very expensive upgrade, particularly if, as RG noted, the bike is old enough to have "French" threading.
Last edited by HillRider; 03-02-08 at 08:42 AM.