Windows xp no more security patches

I don't want to upgrade to the newer version of windows and will not run a mac system since my custom software takes a look at a mac and dies a huge death. (plus it too darn expensive to migrate to a mac machine AND mac os and software replacements) the one machine that I run some of my custom software on is not connected to the internet and it'll never be so that's no worry. one of the others is and it has a 10k cad package that will not run on anything higher than XP, that is unless I upgrade to their new version for even more money. linux distro's are nice but again they don't run my software packages that I paid for so that's out. I see no reason to worry on the non internet connected machines and I do have a win7 laptop for online banking and so forth. I don't use IE(any version) I do like (1)firefox or (2)chrome.
on the internet connected home server unit I'll just use a hot swap drive to boot from to go to the internet and when the special software is needed boot to the xp drive and make sure the internet is off.