Creatine is completely safe. Start with loading 5g 4x/day for 5 days, then maintaining 5g/10g per day, depending on how big a' boy you are. If you just get plain creatine, make sure it's micronized b/c it mixed better, and take it with grape juice. You can also buy it pre-mixed with a delivery solution like Cell-Tech, Phosphagen HP, etc. It's best when taken right after your workout. Taking it before your workout won't make you stronger. There's already a maxiumum amount of creatine in your muscles from loading it. Plus, drinking grape juice before your workout isn't the best idea.
HMB on the other hand.....from what I've been reading on the board, everybody thinks it's crap. The research sounds promising, but then again, it was funded by EAS. Go figure.