I'm using Windows7 Release Candidate build 7100. Downloaded from MS directly.
I'm using AVAST, Adobe Reader/Flash, Silverlight, ImgBurn, MS Office, and IE 8 (which is fine) as well as other 3rd party programs...and no issues at all. Printers, and wireless networks, identified and running.
So tell us.... What build version are you using? And where did you download it from?
And what are these tweaking programs recommended for Windows7? Who recommended them? Frankly, I steer well clear of such 'tweak' programs, simply because of the risk of messing with the Registry, and given this OS is still not RTM final - there's a lot of additional code in the OS that's used for 'feedback' and 'logging'. Any of this code could be compromised by a 'tweak' program, and that could cause all sorts of issues across the OS.
Try a fresh download, a new disc image, and don't put any tweaking programs on the machine, and 'see' how things go. Then let us know if that has solved the problem(s)