im playing d&d 3.5 and im making a wizard with exotic whip weapon but was wandering can i still meet the prerequisite of a prestige class like Abjurant Champion with my exotic weapon Proficiency feat or do i really need a martial weapon proficiency feat instead?
This is a situation where you'll really need to talk to your DM about it. I don't see why Exotic Weapon Proficiency couldn't be substituted for Martial Weapon Proficiency in a case like this.
The reason I asked about race is because some races will give you martial weapon proficiencies free. Elves get the long sword for example (among other things).
"These things also I have observed: that knowledge of our world is to be nurtured like a precious flower, for it is the most precious thing we have. Wherefore guard the word written and heed words unwritten and set them down ere they fade . . . Learn then, well, the arts of reading, writing, and listening true, and they will lead you to the greatest art of all: understanding." Alaundo of Candlekeep
I'd allow it too. Still, there's always the Militia feat from Player's Guide to Faerūn you can grab, though ask your DM because the feat is a Regional one that is usually only aquire at 1st level. It gives you prof. with all Martial weapons.