I have a set of 2000 tahoe third row seats. Can I put them in my 1998 tahoe?

Yes the body style of the tahoe didnt change until 2001. So there isn't a difference between the 98' and 00"

Actually the body style of the Tahoe did change in 2000. 1999 was the last year for the boxier style. Silverados actually went through the body change in 1999. So to answer your question no you cannot put those third row seats in you '98 Tahoe.

Also to reply to your question Tahoe's weren't made with the third row seats. Do you have a Suburban? I have a 1999 Tahoe so I do know that '99 was the last year for our body style.

6 years later so you may already know this or not care, but the Tahoe body style changed in 2000 yet I own a 2000 5.3 v8 4 wd with the new body style and a 2000 5.7 v8 z71 that has the same body style of my 1997 gmc 1500, the reason that is, is because in 2000 gm had Tahoe Limited's made which essentially had the 1999 body style but lowered for use as police interceptors and had the 5.7, as well the Tahoe z71 with the 99 body style and engine but on steroids. I put a third row seat in my z71 just fine, but the Lt would never fit it in.