Moving RAID
 

I've got a fair bit of data that I don't want to lose. I've always backed up my $HOME and /etc but I'd like to set up a RAID-5 to at least reduce the chances of losing some of my more important data that would be impractical to backup completely. Sorry if this question seems stupid but RAID is something I've never played with so I'm just making sure I cover all my bases ;)

My motherboard has a SiS SATA controller that supports RAID-5 which I'm not using at the moment so I'm thinking about getting 4 x 400GB drives for that and setting up my RAID. My question is if/when space because limited, am I able to buy like an 8 port RAID card and move the existing 4 drives to that and not have any trouble losing data? Basically just like plugging a drive into a different port but being RAID, will it be able to sort itself all out on the new controller?

Thanks :)