How did you delete IE?
If you started deleting files and folders then you may have continuing problems because IE is integrated into Windows very closely.
However, if you used Control Panel > Add/Remove Programs, then Add/Remove Windows components, you can always revisit that and re-install IE.
Next, Windows Vista. It wasn't available 'a few years ago', so tell us about this Vista install. Was it an upgrade from XP? If so, I am not sure that Vista's Add/Remove components will work now, or even if it still exists in the same form as XP's Add/Remove components, (I am still an XP user so I know very little about Vista).
You are aware that as IE8 is a Beta that there will be issues with it, and it is only really recommended for testing purposes for people who are prepared to see their OS fail and then troubleshoot that with, perhaps, reinstalling the OS.
It may be best to leave this beta alone.
I heard that Microsoft just updated Internet Explorer and that it was really good. Unfortunetly, I am unable to use it. Here's the story: I got my computer a few years ago and it had IE already on it. I heard about Mozilla Firefox and that it was better, so I deleted it. Here I am, 2 years later, finally wanting to download it again, and I have a problem. When I try and do the setup, it gives me an error that says "Internet Explorer is not supported on this operating system." I have Windows Vista 32-bit Service Pack 1, which should work fine. Is there any way to fix this?
Sorry for the wall of text