you can do both.
IRA limit is $4,000 for last year (2006) and this year (2007).
you can still contribute to 2006, so I would suggest doing that first. Maxing out a ROTH IRA is the best thing you can do after maxing out your 401(k) at least to the employer's match.
In 2008, the limit rises to 5000.
if you have any other questions, send me a pm.