sternpat,
You can rollover your 401(k) to a Traditional IRA and fund a SEP IRA for yourself now that you are self-employed (or a Roth IRA if eligible, or both).

Francisco,
IRAs cannot be rolled back into 401(k)s. You can rollover an old 401(k) into a new 401(k) plan if your new employer's plan allows it. (There are pros and cons to this though.)
You can however, 'roll back' withdrawn funds out of an IRA if the funds are deposited back into the IRA within 60 days of the initial withdraw, without penalty. Check out http://www.investopedia.com/articles/retirement/06/rollovermistakes.asp?viewed=1 for more info on the "60 day rule."