Yes i know my vampire character is at stage 4. However i heard that if you joined the college of winterhold...its members won't attack you, even if your at stage 4. But right when they see me, they attack. The source on the elder scrolls wiki must be wrong then...unless i did something wrong.

If you join at stage 4 and stay at that they are cool with it.
BUT, if you join at stage 4, feed (hence going to stage 1) then go back to stage 4, their attitude towards you will reset and they will attack you like they never knew you.

I know this because it happened to my vampire.

Also, know that before joining them they WILL be hostile, so you must calm Faralda in order to converse with her and join.

crap. I have been trying to feed as little as possible. My vamp character has been one for 14 days, and only fed twice. I was hoping the college could be a place i could buy/sell stuff, even at stage 4. Looks like that's not going to happen, since i joined the college, before i reached stage 4.

Looks like if i want to keep playing stage 4...ill have to sneak in if i want my stuff in my wardrobe...as well as doing enchanting/alchemy.

Yes, I don't know if it's a bug or intended (it mostly looks like a bug to me). I'm talking about joining S4(they're cool) - going S1- then turning S4 (they go berserk like they never saw you at S4 before).

But if you want to stick to stage 4, then join at stage 4 and stay that way for good, they'll have no problem with you.

Is this the same for the other guilds like the Dark Brotherhood, or the Thieves Guild?

Well i hope the bug is fixed then.. After all, it doesn't make sense for college members to accept what you are....then later do a 180 and attack a fellow member. I don't think besh intended for that. Because why would besh allow a stage 4 vamp to join the college in the first place?