Hmmm, seems you have some goals:

1) Owning a home
2) Retirement

First off...CONGRATS...you are starting at a great age that will enable you to build a great portfolio for both of your goals...now the tough stuff, "how do you do this?"

I think you need to look at a couple of things.

1) How much will I need for a down payment? Make that a target for your non-retirement accounts and figure out how much you will need to invest in it for how long (hopefully less than your 7-8 year goal).

2) How much do I have left that I would like to and should devote to retirement savings?

What you have left I would put into the Roth and leave it there. Anything after that goes to the 401k. I generally don't recommend that people withdraw from their retirement accounts for their homes. My personal belief is your retirement funds are for just that...retirement.

If an emergency comes up then by all means do what you have to do but I think you have a good shot at meeting your goals without delving into retirement funds.

You may also want to read pub 590 from the IRS for more details on IRA's...

http://www.irs.gov/pub/irs-pdf/p590.pdf

Good luck!!!