SATA 1-2-3 share the same physical cable. A mechanical HDD can't even saturate the SATA 1 data transfer spec.
With that said, you should still acquire a 300Gbs SATA 2 controller card. The reason for this is, some HDDs require a jumper to be moved, (or removed, forget which), to run at the older SATA 1 speed. Any drive you're likely to buy, will be SATA 2 anyway.
A "RAID" controller doesn't have to be run as RAID. There is a form of RAID called "JBOD" (Just a bunch of discs), which is what you'll be using. You would just install the drivers that come with the card.
What I don't know, is if this will require a reinstall of Windows. RAID or SATA drivers if you will, must be installed from a floppy drive, part way through installing XP. What I would do here is, after you pick out your controller card, see if you can download the instruction manual beforehand. It's always is a good idea to rehearse before the show.
The easiest way to deal with the driver situation is this; if the controller is able to run your SATA drives as IDE, you should do exactly that. Most people who aren't interested in RAID, set the motherboard SATA controller to run as IDE anyway. There's little to no difference in speed, and you bypass a whole lot of aggravation with drivers
Thinking about SATA 3 (600Gbs), is beyond pointless, unless you are using SSDs in RAID 0 configuration.
And yes, I know there are mechanical drives out there conforming to SATA 3 spec. It's marketing BS, nothing more.