What is the maximum yearly contribution to 401k plans?

The limit for a Traditional 401k is $15,500/year, and the limit for a ROTH 401k is $4000/year. However, this year I put $3000 in my Traditional, and $1500 in my ROTH 401K, and Turbotax says I am over my legal limit. There seems to be a conflict in the tax code, so I must be misunderstanding something. Even my payroller and retirement account company are confused.

I think you're confusing 401(k) accounts with IRA accounts. they are different.

For 2007, the 401(k) limit is $15,500 (+$5,000 if 50 or older). The 2007 total IRA limit is $4,000 ($5,000 if 50 or older).

IRA's are totally different than 401(k)'s so make sure you aren't combining the two terms.

There is the possibility that your employer offers a Roth 401(k) in addition to a regular 401(k). For 2007, the TOTAL maximum contribution to all 401(k) accounts was $15,500, or $20,500 if you are age 50 or older.

Sounds more like you contributed to two different self-directed IRA accounts outside your employers offerings. The TOTAL maximum amount across all types of IRA accounts was $4,000, or $5,000 if age 50 or older.

You apparently are claiming a total of $4,500 in IRA's, which would make you younger than 50 if TurboTax is giving you a red-flag.

I would double-check your inputs into the program. are you sure the $3,000 was in an IRA account or in an employer-managed 401(k) account (likewise for the $1,500 amount)? or vice-versa? Those are input on different sheets in TurboTax.