The 401 K is not "with" the company you used to work for, it is with the investment firm that handles the 401K for them. So who is the admin company that was handling this.

You can in some cases live the investment there, or you may move it to your own plan.

Be sure to do a trustee to trustee transfer so no penalty or taxes are due.

To add to what Fr_Chuck said - be sure to keep the 401(k) plan administartor up to date with your address if/when you move. Often times when people change jobs and relocate they forget to do this, and then later on are in a quandry trying to figure out how to access their retirement account. As long as the admin has your correct address, you should be receiving quarterly account statements. You should also look into getting on-line access to your acount, so you can continue to easily monitor it.