If you *do* decide to lance the blister, PLEASE make sure you sterilize the needle first (rubbing alcohol...passing it through a flame can leave soot on the needle).
While you're not wearing your cleats, I'd suggest not staying in sweaty socks any longer than you have to (when I played soccer, we changed shoes/socks as soon as possible after games/practice) and make sure other shoes you're wearing fit well and aren't making the blisters any worse. Clean your cleats too, so they don't get all stiff from mud/etc.
If you have *good* leather cleats, I seem to recall being able to just soak them in water and putting them on, then walking around till they dry. (or maibee it was putting them on, soaking them, taking them off to dry...same general idea).
In any case, buy new cleats as soon as you can afford to...and make sure the new pair does fit properly. Search yahoo for lots of guides on buying a pair of good/properly fitted cleats.
~Ladi