I believe there are at least two ways to do. One is the use of a cross-over ethernet cable as I outlined in #3 above.
The other is to set up an ad hoc network. This is a network of two computers which talk to each other over wi-fi. I would start with the Vista machine. Open 'control panel' then 'Network and sharing centre'. Then click create 'New network'. When the wizard starts choose 'Ad hoc connection' and follow it from there. Both machines have to have working wi-fi units fitted, either on-board or wi-fi dongles.
As Dicke has pointed out, if you have a router it is much simpler to set up. Simply make sure both are speaking to the router then use the Network wizard to create a new network. Again, start with the Vista machine and it should generate a password for joining the network. You then need to copy and paste this password into the network / workgroup on the 8.1 machine.Then you need to specify what files and folders can be accessed on each machine.
If you have a lot of data you wish to move between them, several hundred megabytes and up, you will be much quicker connecting by ethernet than wi-fi.
Edited by Chris Cosgrove, 04 February 2015 - 06:47 PM.