In order to play older games, like Red Alert, via LAN connections on newer operating systems you'll need to emulate IPX connections between the machines.  There are a few ways to accomplish this.

For dos games you're in luck as [DosBox][1] comes with this support natively.  Simply start the ipx server on one machine `ipxnet startserver [UDP port]` and then connect to it on the rest of the machines `ipxnet connect <IP> [UDP port]`

For windows based games you can use something like [Kali][3] which will give you a fairly robust interface, or something like [ipxemu][2] or [ipxwrapper][3] which will trick the games into thinking they are connected via IPX.

[1]:http://www.dosbox.com/wiki/Connectivity
[2]:http://sourceforge.net/projects/ipxemu/files/ipxemu-1.0.0/
[3]:http://www.kali.net/
[4]:http://www.solemnwarning.net/ipxwrapper/