1) If your AUP is current, you should be able to "upgrade". The DS license for v7 is in a .txt file, not a .lic file as in 6.9 (see #2).
2) It should be noted that DS7.0 is based entirely off the the Symantec Management Platform (Notification Server) and is not a stand alone, 32bit install like 6.9. It also doesn't currently support PXE (but will in 7.1 which is in beta).