Bad idea:
1) If you get busted for spamming, you lose both your sites and your link spamming capability. Either a proxy fails and lets through your IP (very common occurrence) or someone complains that yourdomain.com has been spamming them, your host looks at your box, finds SB...
2) You should be hosting your sites on Linux / Unix not Windows! Windows is neither secure nor reliable for hosting sites that need to stay up. No one should be hosting serious sites on Windows.
Don't put all your eggs in one basket.