Can somebody help me with this?

Hi and thanks in advance for reading the post!

I am thinking in buying a RAID card for my PC. Currently I'm running RAID5 on 3 500gb Seagates plus a WD 1tb standalone for backup of the RAID. My current RAID controller is onboard on a Asus P5N-D (nForce 750i SLI) and I am running Vista 64.

I was told that most of the onboard RAID controllers are software based, which means that will use some CPU power to run, plus they are not as fast as a standalone RAID card.

My problem is that I have never bought a RAID card before and I am not sure what to look for. And if this not enough, my MB has only two PCI Express slots (taken by a pair of 8800GTs), two PCI 1x and two regular PCI (one taken by a X-FI). That leaves me pretty much with only one regular PCI slot to use.

Is there any PCI RAID card with 4 SATA2 internal ports that is hardware based and would help me unloading the CPU plus giving some HD performance improvement (even if minimal)??? And something that would not make me sell my left arm to buy it?

If I have to switch my MB to another one with more slots (780i for instance) I probably will give up on the upgrade... So if there is anything out there that you guys know about it, please share it with me.

Thanks in advance!