1.) Click here for information on disabling unnecessary programs and services and, if you want to recovery some of the disk space, click here.

2.) That's how Windows is designed to do it. It can be changed, but it's a long and tedious process, making it easier to rename the current account to something you don't care about, create a new account with the desired name, and copy files/settings over.

3.) I assume this is a 64-bit version of Windows Vista? If so, it separates 64-bit (x64) and 32-bit programs (x86) to clearly differentiate between them, particularly useful if there are 32-bit and 64-bit versions installed, making both required to maintain full functionality. Don't delete, rename, or merge either folder.

Hope this helps,
John