I also have a desk job and recently dropped a good bit of weight (about 40#'s in a pretty short period of time), it may not seem like a lot but I was only at ~210# to begin with... so I dropped close to 25% of my body weight.
I'm no doctor but this is my opinion.
IMO Protein should be used to preserve or gain muscle. It's good to use it while losing weight b/c you don't want to lose too much muscle while shedding fat, which can easilly happen.
The rule of thumb that I go by is 1g of protein per pound of body weight. Also try to spread that through out the day as your body can only absorb (use) so much at a time. Taking too much at one time will probably result is you just pissing it out.
I use GNC Amp Wheybolic Extreme 60, it's costly but has a great BCAA (Branch Chain Amino Acid) profile. I think I'm about to start adding a Casein, which is a slow Protein that is good to take before bed time.
I try to stick to a 45/35/20 ratio (Carb/Protein/Fat)
Hope this helps.