If I remember correctly, you cannot buy RRSP to contribute 2003, because you don't have income in 2002. Check your 2002's notice of assessment, the amount you can but in 2003 should be listed there.
Yes, you can buy but it won't help you to reduce your tax for 2003.
No, if you buy it only for reducing the tax for 2003, because you don't have income in 2002. The amount of RRSP can be taken off from your 2003 income is caculated based on your income in 2002.