I used HP 33S, but didn't bother to program any equations into the calculator. A number of people told me this would really be a good idea, but in my mind this approach suffers from the following:
1. HP-33S does have it's own conventions/limitations in programming equations. The time/effort to go through and figure this out seemed to offset time I could be using to prepare for exam;
2. I like to write my problems out. IMHO, if you come out with an incorrect answer, how are you going to fix it if all you have is ... a number on a calculator. Moreover, you can't see if your units "match" if you are plugging #'s in a calc.
3. When I first started using HP calcs, the solver function would start to have problems converging to an answer based on the complexity of the equation. "oldtimer" It would have even more problems if there were multiple solutions. I know solver functions have come a long way, but I can't help but to be suspicious.
ld timer:
4. I opted for Civil/WR Depth for the October 2006 exam. I felt like preprogramming my calculator would not have added any benefit to my performance. In fact, in some cases, I think I may have been hopelessly stuck with units conversions in a few places. Again, I am a write-it-out look at it on paper kinda guy.
The bottom line, figurtively and literally, it depends on how comfortable you feel with solver function and whether you want to invest the time in programming your calc. '.02'
Best of luck in your preparation.
JR