I have this problem also...
Things that helped thanks to suggestions from people here. (EF is the best thing that happened to my training)
Holding breath while decending > breathing out while ascending > breathing in while up before descent.
Not eating for 3 hours before workout on leg day, even a shake.
Not eating anything heavy at all on the squat day before workout no matter how long before. I found peanuts or PN butter that I love are not good for me before workout.
Have a fruit juice or high carb drink before and during workout.
Cardio in general makes squatting easier.
All other compund exercises in general help build up the resistance to this feeling.
The glute machine also makes me feel somewhat dizzy for some reason but these days I am used to it and it barely effects me. (Maybe add this machine to your routine)
I found that I have to pace myself. Do easy weights with easy rep range and stop when I am a bit dizzy. each workout I can do more without getting to dizzy. Just about 2 weeks ago I was really feeling shit from squats and now I can handle it much better so all the advise seems to be working but am still gonna give it a few more weeks and add more weight to see how much better it is.
I also moved my squats away from begginging of workout. Will start with chest, shoulders, arms, back, whatever else it is I am doing that day yet try to even it out so I am not to wasted by the time I get to the squats. can be tricky if you are only doing legs or legs and one other muscle group that day. If so then maybe start of with 1-2 warmup sets of leg extensions or really easy squat sets... maybe lunges...
Ok, so I am never working at full capacity for squats but I will get there eventually and I am still getting stronger and my legs are growing. Overall much better now.
Here is the link to the thread that I started on the same subject.
http://www.elitefitness.com/forum/showthread.php?t=348466