"Is it legal for me to send  the disk to someone else who wants it? Am I required to delete MY V3 from my hard drive if I give the disk away?"

Giving away the disk while keeping a duplicate of V3 would be like distributing the installer.

The disk was part of a limited promotion, like DAZ once giving away all 1st/2nd/3rd and 4th generation figures for a short time.

The promotion has ended and DAZ is now charging again for older figures while giving away Genesis 1 & 2 instead.

So, giving away V3 would sabotage their attempts to wean people off of older figures and make them try Genesis instead.

You might be still allowed to sell or give away the disk depending on the consumer laws of your country, but I'm pretty sure you then would have to delete everything you installed from that disk from your computer.