Moving from RAID0 to single HDD

It is pretty much that simple. You just need to mirror the array to a single drive using something like Acronis True Image. You need a third drive to do it though.
Why is your array so slow? What drives are you using, what motherboard? I am not saying running RAID 0 is a good idea, because really it's not. A fast single modern drive will be faster all around than a couple of older drives in RAID, but the drives in RAID should still be faster than the same drives not RAID'd. Perhaps you don't the array configured correctly, or maybe using the wrong driver?

Motherboard is MSI K9A2 Platinum using the AMD SB600 controller.

Hard drives are pretty old now, I'd imagine just over 2 years, they were bought at around the same time but I didn't try putting them in RAID until the beginning of this year, it may be the drives, but on their own, they seem relatively fast, neither have had any bad sectors or anything.

Like I said, the main speed decrease is on boot up, getting past POST and reading the RAID setup. Surely this wouldn't be the fault of the hard drives but a slow RAID controller?

Thanks for your answer though, Acronis costs £25 though, that's over half the price of the new hard drive itself   are there any less costly pieces of software around that anyone knows of?

Slow boot up can be cause by so many factors on the HW and SW. If you have a lot of programs checking for updates on the internet for driver updates it slows down boot up considerably. You should check the boot up sequence of your pc and remove the un-neccesary update software.

I own Acronis DISK DIRECTOR amd i always maintain an image copy of my drives including c:\. Moving my OS to any drive or RAID is very easy and quick. It is worth the investment.

There may be a trial copy that you can use. Also there are freeware that provide similar functions(if not all). Theres a lot of information on the net pertaining to this.

The steps will be:
1. Complete backup of the data on the RAID0 array (seen by Windows as one disk) to another device, then VALIDATE that backup to be sure it is good.
2. Break the RAID0 array to 2 separate HDD's using your RAID management utility.
3. Use Disk Management in Windows (or some other tool) to go to each of the 160 GB HDD units and Delete their Partitions. Then on each, Create a new Primary Partition the full size of the drive, and format it with the NTFS file system.
4. Restore the data from the backup to one of the HDD's.
5. Use the other for data.

Now, some wrinkles along the way. What new device? If you have a spare HDD (or can borrow one temporarily), that will do. If you must buy a new one (you'd end up with 3 HDD's), maybe even better, but not free.

What backup software? Well, IF the HDD you are using to receive the backup data is by Seagate, you can download their free utility Disk Wizard. It is really a custom version of Acronis True Image that will make a CLONE of the entire contents of the original "drive" (i.e., RAID0 array) to a Seagate HDD only AND make it a completely bootable unit ready to take over as the C: drive. On the other hand, if your new (or borrowed) HDD is by WD, their version of the same thing is Acronis True Image WD Edition. So you could get free cloning software to make your "backup" (really, a complete clone). The problem is: next step is to make a clone AGAIN, but this time TO one of your original 160 GB HDD's. The cloning tools I just mentioned only make clones TO either Seagate or WD units. SO, if your existing 160 GB units are from one of them, you can use their free utility to do the second round of cloning (AFTER you have transformed the RAID0 HDD's into two separate units) back to one of your 160 GB units to become the final C: drive.

Small bonus if you can get / use one of those cloning utilities. Each is MUCH more powerful that just making clones. One very simple kind of task they can help you with is in those steps of Deleting old Partitions, making new ones and Formatting them. May be even easier than using Windows' Disk Management.