Mark:
I realized that my post didn't answer your first question, which asked what the Roth IRA is like as an investment vehicle.
It is basically an investment account which you cannot withdraw from (without penalties applying) and against which you cannot borrow. In almost all other respects, you can do anything with the money in it that you want.
You could operate it like a 401(k) if you wanted. It sounds like the company you work for provides a selection of x number of mutual funds and it is up to you to choose which ones and in what percentage to purchase and they take care of everything.
There are, as mentioned by a previous poster, literally thousands of people willing to help you do almost anything with an IRA (for a price, of course). Go to Forbes.com and search for "Kinky IRAs" to get a feel for some of the more unique things you can do with a Roth IRA.
If you are not interested in actively managing your IRA and you want it to act like your 401(k) plan, find out which mutual funds your firm invests your money in and look around on the internet for an on-line broker that permits you to open a no-fee IRA with a wide selection of no-load mutual funds. Check to see if the funds are the same and invest the money in your Roth in those mutual funds and forget about it to the same extent you would forget about your 401(k). When the time comes to make your next contribution to your Roth, simply send them another check for $2,000 and purchase the mutual funds you are interested in.
For someone starting a Roth IRA from scratch (I'm in the same boat), investing in no-load funds at an on-line brokerage would be a very cheap way to be invested and it would act very much like your 401(k) plan except that there are usually no automatic deductions from your payroll to fund it.
On the other hand, there are some places that will allow you to set up an automatic debit from you checking account as a means of funding your IRA. This would probably be less painful than writing the $2,000 check and it would provide the opportunity for dollar-cost averaging over the year. I think that there are some on-line brokers that will do this for you. If they do, check the fees.
An interesting resource for you to investigate when looking for a broker that suits your needs is
www.gomez.com -- they have a broker scorecard designed for consumers to use. Also see the area on selecting a broker at the Motley Fool (see fool.com).
I hope that this helped you more than it confused you.
Guacamole