I have posted about this once, but I have gotten no responses.  I have read some responses on this before, but I didn't get a definitive answer from those posts.  When I enter the current temperature in my FMC, if it is not a negative value, the arrival times go nuts.  What can I do to prevent this from happening?

If you are talking about the T/C OAT on the PERF INIT page, that is a Top of Climb Outside Air Temperature which should always be negative unless you are cruising at a really low altitude. This entry is also optional.

Ah, I misunderstood that.  I thought it was the current OAT at ground level.