I had the same problem about pressing the two buttons at once. It worked fine when I held down pgup whilst pressing the other relevant buttons.
I think you need Tifa in your party, on disc 3 (haven't got there myself on this current install, so I can't say for sure).
The sequence I was told was different to yours. It sounds right, and gave me the 1 gil stash when I played it early on:
[cancel], [switch], [menu], [pgup] + [menu], [pgup] + [switch], [cancel], [switch], [menu], [pgup] + [cancel], [OK], [cancel], [switch], [cancel], [start].
Am I horribly ill-informed, or is this the correct tune?
Edit: Well, the tune I got given worked for me. PC version, original CDs, etc. Not that I can use it, given that I avoided using Tifa whenever I could.