Difference between Traditional IRA versus a Roth IRA. The traditional is pre-tax contribution, but will have taxes taken out when you make the withdrawl, plus any applicable penalties if taken before 59 1/2. Roth IRA contributions are post-tax earnings, meaning you can't deduct them, but the money in the Roth, including earnings/interest, are tax-free, and as long as you've had the IRA for at least 5 years and are over 59 1/2, no penalty either.
Difference being tax-DEFERRED (Traditional IRA) versus tax-EXEMPT (Roth). Either will allow withdrawls up to $10K for first-time homebuyers.
And if you're willing to pay taxes (but no penalty) you can roll over your Traditional into a Roth if so desired and you don't take too big of a hit.
There are income limits to IRA's which I'm not entirely sure of, but IIRC, it's about $105K for single and $165K for married couples (above that no breaks.)
As with 401(k)'s there are contribution limits based on whether you're over or under 50 years of age. For an IRA (traditional or Roth) it's $5K if under 50, $6K if over 50--but that's combined, so if you have one of each you're limited to $5/6K for your total contribution to both accounts. Compare this to the max 401(k) contribution of $16,500 if under 50, and $22,000 if over 50.
BTW--there are also Roth 401(k)'s. Still with me, right? Simple, ain't it?