See the Securities subforum: http://bitcointalk.org/index.php?board=78.0
Maybe buying your own miner will become profitable once more in the future but right now the prices are a bit steep.
If you want to buy a GPU miner I suggest mining altcoins such as Litecoin and GLDcoin. They can't be mined with ASICs.
How long does it take to get that all done for registration and purchasing?
Purchasing shares is very easy.
There's Bitfunder, Btct.co and Havelock investments.
Personally I use Bitfunder but it requires an extra account at WeExchange.
Take your time to choose.