Air Conditioning - Adjusting or re-directing air flow in office A/C vent

Our office has one of the worst distribution of air flow among the vents, one would blast cold/hot air (depending on temp) while others would barely have any draft. When I asked the landlord to fix the A/C last time, when it stopped blowing any, I don't know what they did, but they messed with the circulation. Now my office is gets all the heat and it blows right toward my desk. You should see my office, I have a big floor fan and humidifier trying to keep the air moist and cooler...

http://img97.imageshack.us/img97/6738/img00206j.jpg
Approx 22"x22"

Question, I remember they adjusted some handle or knob under one of the tiles. I can probably try that myself, but I would have to re-adjust it when summer comes.. Instead, does Home Depot sell anything I can cover and redirect the flow towards another direction? I heard covering these vents can be hazardous somehow.

PS: I tried taping a big cardboard on the vent, it did not hold it. Even with heavy duty tape. The flow is really high.

Thank You.

does not look like there is a damper in the grille so yes you will have to get above the ceiling.

Thanks. I will remove some tiles and check out what we can do.
Will post pictures for you.

You can fill in 3/4 of it with cardboard tucking it under tiles , not recommended that all vents to be done on this system !!

I wish they sold some metal aparatus that I could screw onto this that is shaped in a way that the airflow would be directed in certain direction like a very short duct. Ever side could be sealed except one side, the side that would direct the air away from me or towards the door so it would blow out my office.

You might be able to move the grille over a tile or two if there is enough flex. Also they sell directional grills that you could install to move the air to the door.