You can install AROS on to a PC's hard disk and boot it directly, but you can't play any of your old Amiga games on AROS. You can install UAE inside AROS and use that to play your old games, but to be honest you would be better off using WinUAE as it will probably be faster and better supported than the version of UAE which is available for AROS.
You should look at the KXLight version of Amiga Forever. It's a bootable CD which basically contains Knoppix (a small version of Linux) which then immediately loads Amiga Forever. This way you can boot directly in to an emulated AmigaOS which will be capable of playing your old games. There is no reason why this could not be installed to a hard disk, but it may be a bit complicated.
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moto