Yes, if you sync with the library of the other computer it will replace your songs with the songs of the new computer.
As of now, no. There has been rumors that in iOS 5, this can be done.
Go to songs and swipe your finger across the song you want deleted
nope
Yes, as long as you have ever used the iTunes to sync files to your iPod Touch, even if the device is lost or you accidentally deleted or wiped out the data, you still have chances to recover those precious deleted files. If you have made backups on iTunes or iCloud, you could use a third-party tool like PhoneRescue to get back your deleted songs on your iPod touch. For no backup, you can still use the tool to retrieve songs directly from device.
Not directly, but you can put the songs onto a computer and then transfer the songs from the computer to the phone.
If you already have the songs on your computer you just simply need to sync your ipod touch with your computer.
download songs on to your computer, then upload them to your ipod
Connect your iPod to your computer using a USB and iTunes will automatically sync your songs.
if you plug your iPod into your computer it will sync your music to your iPod. Or you can buy your songs with the iTunes app on your iPod touch.
When you unlock a passcode that has been forgotten on your iPod Touch, all of your songs will unfortanetly be deleted, and you will have to put all of them back on. But if you are CHANGING your passcode, off of the settings button on your iPod Touch, nothing will happen to your current memory.
threw itunes
Using iTunes and your computer.