The oboe squeaks whenever I tongue the notes below E... and saliva gets into the reeds when I tongue continuously for a few times. How do you stop your saliva from getting into the reeds???

There isn't anything wrong with saliva in the reeds. This is ok. Just suck of the saliva. To play notes lower than Middle Staff Bflat you should gradually lower and loosen your jaw. Don't "bite down" on the reed or you'll get a very bad sound.

relax your embouchure more, don't "bite" the reed. Make kind of a face as if you were whistling. Also, in terms of spit, obviously, you want some moisture in your mouth, but make sure you don't have a ball of spit bunched up thats just ready to make your oboe sound raspy. Also, it might help to play more on the tip. this should help both problems.

I was having the same problam when I first started out and my teacher told me to get the low notes out to make kind of an O type shape in your mouth like your saying "oh".

ALWAYS make an O with your mouth. the thing about human mouths is that when we try to form an "O" we make the perfect shape for a seal on the reed.
Spit? just don't spit into your reed. Water will collect in there anyway, but it can be blown out, and should be after you finish a piece.
tounge squeaks? ask someone to lengthen the tip of your reed. soak for at least 1 minute.

alex

<Added>

OH and when attempting low notes, dip your head slightly.