Is your lbs Silverters? 
Telling you it can't be done isn't very helpful really.
To add to all the valid points above - think about how much you want to change the bike. Modern forks will alter the handling; lack a canti hanger which would mean a change to V brakes. That'll involve changing brake levers too, and if you have STis, then the gear shifters as well. All that on top of the fork, headset and stem change.
My favoured option would be to stay rigid, or find a period fork (up to 96/7) either in the classifieds on here or e-bay. There's plenty out there for not much money.
Good luck!
Telling you it can't be done isn't very helpful really.
To add to all the valid points above - think about how much you want to change the bike. Modern forks will alter the handling; lack a canti hanger which would mean a change to V brakes. That'll involve changing brake levers too, and if you have STis, then the gear shifters as well. All that on top of the fork, headset and stem change.
My favoured option would be to stay rigid, or find a period fork (up to 96/7) either in the classifieds on here or e-bay. There's plenty out there for not much money.
Good luck!
