I wouldn't worry too much about condoms when having oral sex, as long as you haven't any open wounds in your mouth, and the guys penis hasn't any broken skin you'll be fine.
Just enjoy! :O)
I agree, but will provide a little more data.
Saliva is not infectious. Not only is saliva not infectious, but there are enzimes in saliva that cause HIV to no longer be active (viruses aren't "alive", they are either active or inactive). Receiving a blowjob is completely safe as far as HIV is concerned.
Depending on where you go and whom you ask, there's a broader range of opinion about giving head. Part of this comes from science, which resists words like "always" and "never" or concepts like "100%". These are not part of scientific method, which allows for extremely unlikely probabilities which are unrealistic in the real world. Another reason is that, especially in today's prohibitionary climate, reassurring someone that giving head to a guy is "safe" is seen as akin to endorsing oral sex, which the American Taliban will never accept. Hence you'll see "low risk" where you really should see "no real-life risk".
Remember the part about saliva having enzimes that inhibit and render HIV inactive? The only way for someone to be infected via sucking cock is for there to be no saliva present in his/her mouth. This seems highly unlikely to me, but occasionally someone can get so tweaked on Meth that their salivary glands shut down. But partybois are notorious at giving lousy head, and with Meth Mouth a factor, who'd stick his dick in that hole anyway?
The only other possible situation where giving a blowjob might pose a risk is if you've just had oral surgery. If you've ever had a tooth pulled, I think you'll agree that this is also an unlikely scenario.
A few other things to keep in mind:
1) In order for you to be at any risk sucking dick, the guy you're with has to be HIV+ and have a very high viral load. Regardless of what you may hear or think, less than 5% of the gay male population is HIV+. The odds are in your favor, though, of course, the risk will always be yours to take.
2) This only applies to HIV, which is a very fragile virus. Herpes, HPV and all kinds of nasty bacterial STDs (Syphillis, Ghonnoreah, Chlamidia, etc) can be passed though oral sex, both giving and receiving. It's your risk to take, as I said above.
Good luck and have fun!