Try them on first. Some people (like Fetou) dislike the clamping pressure. I personally find them very comfortable, but they are noticably more clampy than most open 'phones. This is by design, as they need to clamp to get decent isolation, which they have in spades. I use mine to listen to music on the bus, and it cuts through the hella-noisy bus engine easily.
HD280s are meant to have a flat frequency response and as such are VERY light on bass. You'll probably have to equalize them quite a bit. The bass part of my iTunes equalizer is more a mountain than a molehill, but the 280s can keep up pretty well.
As for the sound card... I'm sure most sound cards will have a better DAC than what I assume is a cheap on-motherboard card that you're using. Plus, many Creative cards offer a headphone mode that adds some crossover. I'm not a huge fan, but may make a difference in decreasing the inside-the-head feeling.
Have fun with your 280s! They're my first serious cans, and I'm already planning some upgrades when I get the $$. Welcome, and I offer my condolences to your wallet.