Hp pavillion will install LAN drivers "from the box" no probs.
Use GPARTED (freeware) to format / partition your HDD(S) and then install W7.
Make the LIVE CD BEFORE wiping your computer.
GParted -- Live CD/USB/PXE/HD
You'll certainly have LAN connectivity and you should be able to get any missing x-64 drivers from the HP site --HP are one of the better companies in providing hardware upgrade info.