windows xp 32bit extended memory switch

Hi. I'm gonig to upgrade to 4-6gb memory, and I know XP 32bit can only see 3gb, but there is a boot.ini line htat can be edited to see more. can anyone tell me what it is?
I am planning to rebuild to W7 when I can afford to, both moneywise and timewise. But need this info for the present
I am planning to rebuild to W7 when I can afford to, both moneywise and timewise. But need this info for the present