My girlfriend approves of my hobby, and is mildly interested (moreso in the new things I build, or projects like the AM transmitter I built for listening to mp3s through her 1934 RCA console or Nixie clock), but mostly just acknowledges that it's something I like to do. I don't spend lots of money on it, and very often I end up selling things I've acquired to buy things that benefit both of us, like parting with my last Rev 0 KIM-1 so that we could purchase supplies for working on our fix'r up'r house. Even then, she insisted I keep part of the profit for something I wanted (in that case, the train ticket + admission ticket for The Next HOPE).
Like Saundby said, you have to go into a relationship being who you are, and making who you are known. I don't expect anyone to be completely interested in my hobbies, but it wouldn't be right to ask me to give up something I enjoy as long as it's not hurting the relationship. It's a two-way street with us, though; for example, I'm not all that interested in swing dancing, while my girlfriend really loves it. While I may not want to go to events with her, I fully encourage her to go with friends when she wants to!
That said, she's probably more tolerant of old computers than most...she's going with me to VCF (her decision, mostly for the old games) and recently asked if I could connect an old green-screen serial terminal to her Linux workstation for writing/editing code with less distraction/eye strain. I don't think many women actually /want/ a serial-attached dumb terminal sitting on the desk in the bedroom!