+0
Doing X is different from doing Y.

If I converted the first 'doing X' to the infinitive as:

To do X is...

how would the rest of the sentence be? Would it be:

To do X is different from doing Y

?
+0
Either can be used. The infinitive form usually does not read as well as the -ing form, in either position.
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
Mister MicawberEither can be used. The infinitive form usually does not read as well as the -ing form, in either position.

When you say 'Either can be used', do you mean either 'To do X is different from doing Y' or 'To do X is different from to do Y' can be used?
Well, the 'either' I was thinking about was:

Doing X is different from doing Y.
To do X is different from doing Y
.

These are the forms that are often discussed on these forums. I don't see anything grammatically impossible with doing is different from to do or to do is different from to do, but I just don't think it's done.