If I have a -1/-1 on a ceeature (due to infect or something to that effect) and I put two or so +1/+1s on the same creature, does that creature still have the -1/-1 technically?
No.
Before any player can take an action, the -1/-1 counter and one of the +1/+1 counters annihilate each other. The creature will have only a single +1/+1 counter on it.















