Sounds like your 5th gear synchro is on the outs.
My hubby had the same problem with his.. we now have an ACT clutch and lightened fly wheel with a 4th gen JDM tranny with LSD!!!!... SWEET!

But the 5th gear synchro isn't an uncommon problem for Base models... more specifically I think 97.

Also I have found that when you have problems putting the car in Reverse... try pumping the clutch again and putting it in 4th and then reverse. I used 4th because it puts less strain on 1st and increases the long-gevity of the clutch.

When its cold the Tranny fluid is cold and the gates are cold.

I used to have a 4th gen and I would stop at a light and then try to shift and the stupid car wouldnt go into gear.. I Thought my clutch was FUBAR'ed.. but it was just the master cylinder... replaced that and no more problems.