There is a VM of mynode out there but it needs 4GB so you can't run it (well) on a machine with just 4GB.
Since it's Windows 8 I am guessing it's using DDR3 RAM which is cheap now.
Same with SSDs you can get a 512 GB SSD for under $75 and a 1 TB for under $110 (US based pricing)
Side note, so long as it's a legit copy of Windows 8 you can still do the free 8 to 10 update from Microsoft:
https://www.microsoft.com/en-us/software-download/windows10
If OP insist to run myNode on his old PC, using Linux have major benefit because it uses less RAM (which means more RAM for myNode) & VirtualBox can take advantage of Linux paravirtualization (which increase myNode performance).
Ubuntu repository doesn't provide Bitcoin Core. You need to add PPA which provide Bitcoin Core. However both PPA (https://launchpad.net/~bitcoin/+archive/ubuntu/bitcoin & https://launchpad.net/~luke-jr/+archive/ubuntu/bitcoincore) i know provide outdated Bitcoin Core.
Besides, OP already mention he want something similar with MyNode.