You're lucky that it works at all!
Mine was - fortunately - free with a laptop and it has only worked twice.
When it did work though, it was fairly quick at over 300Kb per sec, which is what it should achieve on 3G. On GPRS, it will be a fair bit slower but nowhere near as bad as what you have experienced.
Your card is almost certainly faulty. I may still have the direct contact details for the 3G card tech support department - if I can find them, I'll post them here tomorrow.