Desktops have a different memory (RAM) type and size so you can't physically swap the memory. Also, they keep changing the RAM speed so your notebooks may be using different RAM speeds even if they have the same slot configuration.
If you are talking about reallocating memory (RAM) over a network I don't think so.
You can, of course, easily swap files over a hard wired computer network or wi-fi network (and transfer at high speeds) if you set it up properly (and you can get a great wi-fi router for under $50).
Also, you can just buy a $30 USB 2.0 Flashdrive and easily swap files (acts as a hard drive when plugged into the USB 2.0 port) by downloading the files onto the flashdrive from 1 computer and then loading it onto the other computer.
You can now get 1GB Flash drives for under $50 on sale (after rebate) or 256mb models even as low as 19.99 after rebate (and 512mb models for 29.99 after rebate) -- these are extremely versatile as they are solid state (no moving parts like a hard drive) so the data is not lost. Some of these like the Lexar Jump drive secure even require a password to transfer files off the drive for security.
Computer manufacturers keep changing memory (system RAM) types and speeds not only for speed improvements but also so you can't just keep taking your old computer memory and use it in a newer computer. They want to keep selling you new product.
I have 2 notebook (1 and 2 year old) and a desktop( 5 years old) and i want to know if i can transfer memory and hard drive space from the desktop to the notebook and vice-versa.