It's definately possible but not very easy.
Solaris can handle a network install (Sun call this a 'jumpstart' install), but traditionally, it's done from another solaris system.

What you will need is:
a tftp service running on your windows box that has a copy of a solaris 'miniroot' (obtainable from the solaris install CD/DVD) - pretty much just a solaris kernel and the bare minimum additional files.
a NFS service providing an image of the solaris install CD/DVD
a dhcp/bootp server that can listen for the sun server's MAC address and reply with all the network information it will need, along with the tftp server location to get the miniroot, and the nfs server location to get the install media from.

Then it's just a matter of booting the sun server with 'boot net -- install' from the OK prompt.

You should be able to debug most problems by running a network snoop (such as ethereal) on your windows server to watch the various hadnshakes occur.

It's also worth having a hunt on the web for 'solaris jumpstart from windows server' or something like that to see if there's a first hand account from someone out there.