Your memory: Nothing, depending on the capacity of your computer's RAM, Vista may affect it, then again, many operating systems do, however, Vista has been criticized for it's high usage of memory.
Your Files: Depending on the way you install the operating system, if you upgrade from XP to Vista (Vista only supports XP=>Vista upgrades), your files will be perfectly fine, if you allow the installation to erase the contents of the hard drive and partition you install it to, your files will be lost.
If you'd like to see if your computer can handle vista, see related links.
You can compress your files into a spare harddrive to keep your memory ok
Limewire is one of many download sites. The size of files on download sites varies with what the file is. Large files will take up a lot of memory, small files will take up a small amount of memory.
There are 5 files in Windows 7, but DO NOT tamper with the system because it can damge your files and erase memory thinking that it is an online hacker.
You can't download files from the internet anymore, unless you have another download manager or browser w/ download manager..
Yes.
Look in the temporary internet files on the hard drive of the computer to find the cache memory in windows 7. There you should be able to see the cache files.
There is not a way to download linked files to window media center. This is part of the computer software.
Download a converter.
if you download it onto your hardrive you folders will be fine but if you download it and reformat the system all you files will be lost so i would advise to put all your folders onto a internal hardrive (portal hardrive or a memory stick) i also wouldn't advice downloading vista because i had vista for about a year and it started to randomly i would advise downloading windows 7 or buying it :/
Download the free software winrar to read ear files and some other compressed files
OGG Files are media files - more specifically, they are sound files. You need to download a codec for Windows Media Player for .ogg files, or you can download an alternative media player like VLC Media Player.
Go to www.skype.com, download the installation file for windows. The installer will automatically recognize version of your OS and install required files.