Intel finds themselves in an interesting position. Normal they develop the technology and licence it out eg MMX, SSE etc
This time AMD has come up with x86-64 instruction set. If Intel want to use this technology, my understanding is they would have to pay for it.
Intel could use their leverage and get a deal out of this next time AMD wants to use some of their technology but AMD is moving away from Intel so i see this as unlikely.
Intel i believe will wait and see the market penitration of x86-64 before making any descision, partly because they do not have a consumer 64bit ready for the maket place.
Intel have marketshare and i beleive they will respond with their own version of a hybrid x86-32/64 bit chip.
If and when Intel does, software will start appearring for it much faster than for AMD's x86-64.
I do not see 4 windows versions as microsoft will incorperate the intels version as the standard (eg you will get winxp with winxp-intel64 as a package or more likely the winxp 32 bit will disappear altogeather and older versions will be made incompatable so you have to get a new copy of thier operating system).
Intel within 12 months of release of a hybrid cpu, would remove all non 64bit chips from the product range so all new intel based systems would have 64bit compatability. this is a huge market share and with Intel's advertising would really push 64bit computing into the home.
As long as hardware and software can run in 32bit mode Intel can come to the party late and enforce its own standards.
How many programs are wirtten with AMD's 3dnow etc? even they had to licence SSE.
AMD will spend the money telling the world that you need 64bit computing at home and when Intel are ready, will agree with their own product range. Joe Consumer will see Intel, see 64bit and and think wow i gotta have that!
Side Note: from intel's piont of view it is a shame that their hybrid chip couldn't link x86 to I64 and thus help the tranisiton to getting everyone on I64 as intel has spent a fortune on itanium I64 cpu development.