Actually, this has, mostly, already been implemented...
This is exactly what Microsofts "Trusted Computing" is actually, specifically, designed to accomplish. Additionally, "Vista" already has most of the technology (APIs, secure media-paths, software-signing, etc.) already built into it. So does the "Mac", though Apple is apparently leaning more towards a hardware-approach ("TPMs", etc.).
Furthermore, the ability to refuse Internet-connections to any "Non-Trusted Computer" is already built into most of the routers, already in use, by most ISPs. So, if you arent running this control/monitoring-hardware/software, then you simply will not be allowed to access the Internet, at all.
And, any thought that the U.S. Government would, in any way, try to impede this plan... is utter nonsense. The simple fact is that the U.S. Government is not only, not opposing this eventuality... It is actually one of the biggest proponents of this entire monitoring/tracking/control scenario. In fact, laws imposing this very type of scheme (on ISPs, colleges, etc., for example), are already being created, and passed.
Another interesting couple of points is that, Microsoft actually started working on this very, all-controlling, all-seeing, "Trusted Computing platform" plan... just about the same time that the White-House apparently ordered the DOJ to drop the Anti-trust prosecution against the company (...after Microsoft was, in fact, found "GUILTY", and right after every one of Microsofts appeals were rejected by every court, up to and including the U.S Supreme Court). And "AT&T" (the largest single internet-access provider in the U.S., which has just announced its intentions to intercept, and monitor, all Internet-traffic for various "legal" and "copyright"-related, reasons) is set to be given full-immunity (by the Federal Government) for its various illegal-activities (with regards to AT&Ts, illegal, warrantless-spying on customers)... But, these are probably all just amazing coincidences... Right..?