Mutual fund IRA rollover vs. Roth IRA : which is the better move?

Last year, I rolled all of my investments from the 401K plans of previous employers into a mutual fund IRA rollover account. I have recently been considering putting that money into a Roth IRA. I would not be contributing regularly to the Roth IRA, were I to do it.

What are the advantages and/or disadvantages of doing this? Is my money as likely to grow as it would in a mutual fund investment? What are the tax issues involved with such a move?

You are not able to do this type of rollover because when you contribute to a 401k or a traditional IRA these funds are contributed on a pre tax basis where as a ROTH IRA funds are contributed by money that has already been taxed (like the money you take home from your paycheck)
The tax differences are when you take money out of a 401k since that money was contributed pre tax (the contributions came out of your paycheck before the taxes are taken out) you have to pay taxes when you are ready to "cash out" your 401k but here's the kicker. You pay about 20% federal taxes on the amount taken out (depending on your tax bracket or what the taxes will be at the time you take the money out) plus, if you take your money out before you are 55 and retired or 59 and still working then you taxed an additional 10% early withdrawl penalty.....so a lot of your money is gone to taxes.
ROTH accounts are contributed by money that is already taxed so that when it is removed you may only be subject to the early withdrawl tax but no state or federal tax.
But back to the original questions, since one is a pre tax contribution and the other is post tax you are unable to combine them in one account. Even if you suggest making up the taxes or whatever it just doesn't happen, anywhere.
You can contribute more money per year into a 401k plus you may also receive employer match.
You can diversify and have both an IRA and ROTH IRA...speaking w/ a financial advisor is your best bet :-)

A rollover IRA is like a temporary parked account into it can be transfered into another 401k or you can just leave it there....

a roth is a personal IRA account that is tax defered...

with either account you can invest in ANYTHING you want including mutual funds, stocks, bonds, money market, cds, et cetera

I would suggest consulting a tax professional but you should be able to convert to a Roth IRA.

However, there are immediate tax consequences as you will incur income taxes on that money. Depending on your age, that can often make sense. In a traditional IRA, you pay no income tax now but pay income taxes as you withdraw funds, in the Roth you pay income tax on what you put in now put pay NO income taxes on any of the money when you withdraw (normal retirement age)