Thanks for the info; we would only do this when we had low to no other income, so this is good to know.ssimps - You can withdraw money from your RRSP any time you like.
Basically any withdrawal you make will get added to your taxable income for that year. There aren't any penalties per se but if you do a withdrawal in a year where you already have a high income then you will get nailed with taxes.
All rrsp withdrawals are subject to withholding taxes - this is not the final tax bill but just a tax credit.