Hrm...it doesn't sound like a good idea to me. What ppi are we talking about?
I work in 300 ppi with no probs (512 mb ram, P4 2.4 gig processor) and 300 ppi prints out beautifully.
The thing is, if you start small and then enlarge the program has to "fill in" the gaps. That will lead to greater visual pixelation.
I've also worked in 150 ppi and that prints out ok too.
Wish I could be more of a help.
Suzanne