I'm sure you can upload an image, just not attached specifically to that post. Head over to the gallery, upload your post, and then when editing your post, there's a My Pics link to the lower right which allows you to add your pics to the post.
And it sounds like it might be a driver issue. What graphics card are you using? And do you know what driver version? Both ATI and NVIDIA use packages that envelop most cards out there these days. For ATI, its the Catalyst Drivers and for NVIDIA, its the ForceWare drivers. Try updating your drivers, if you haven't already and see if it makes a difference.
If you've got an Intel vid card or something else thats integrated with your motherboard, you might be outa luck. MA generally won't support onboard graphics, or at least they didn't before. If the updated drivers don't work, give support a hollar, but you'll be lucky to get much more than a cut/paste "Upgrade your vid card" answer.