When you run the Windows 7 install, right at the beginning you can choose Custom Install. In that area, there will be an option for formatting the drive, deleting and recreating partitions, etc. If you want to totally wipe the drive and use it all for Windows 7, then delete all of the partitions and create one new partition for the entire drive; then format that partition.
As for the internet connection: The best way to deal with this issue is to find and download the driver before you start the process. Another way to do it is to wait till after you have installed Windows 7, and then try to connect to the internet. It might work, but it probably won't, so you'll probably have to get an Ethernet or wifi adapter for the computer which will work with Windows 7. If you have an extra one laying around, you could wait till after you do the Windows 7 install, then temporarily install the extra adapter. Then do a Windows Update. If you find an update for the built-in adapter, install only that one update. Then shut down, remove the temporary adapter, then power the computer on. This "Windows Update" method has never failed to work for me.