By "Taxable IRA", I assume you mean a deductible IRA; that is, one in which you took an income deduction for the amount contributed.
You can take tax-free distributions from the Roth IRA independently of anything else. Easy.
For the IRAs, think:There's no such thing as two different IRAs. You only have one big IRA, which might be spread over multiple accounts, and which might have come from deductible or non-deductible contributions. But it's all one big IRA to the IRS.
The distributions are considered to come proportionally from the deductible and non-deductible parts, in proportion to their balances -- regardless of which account you take them from.
The deductible part is fully taxed; the non-deductible part is tax-free up to the amount you contributed, then fully taxed after that. In other words, the withdrawal is assumed to come from the contribution first, and the "earnings" are not touched until that's gone.
Just to correct a misconception: Don't call it "capital gain". The taxable amounts are taxable as ordinary income, not at the lower capital gain rates.
I'm sorry, I can't help you with the 401(k) part of your question. I think I know how this works, but I don't want to give you wrong information.
