Not totally cold but how cold and safe is it? If I put my btc in a wallet in a pc but never connect it to net unless i need to use btc, is it practically cold storage and how safe is it?
It depends!

The problem is that almost all PCs are relatively unsafe. As Bitcoin use becomes more widespread and Bitcoins more valuable, we'll probably soon see more malware looking for it. Naturally, if you limit your internet usage, you are less exploitable. Yet only one such malware need to make it onto your computer, and then connecting even once to the net may be enough for your wallet to get stolen. Also be aware that what counts may not be that you think of yourself as having connected the computer to the network, but rather that indeed no potential malware (say a rootkit able to hide its network connections or something having infected your interfaces) can talk to anything outside your computer. Think unplugging your network cable and physically removing the wireless interface, rather than "I clicked to disable it, and I think that might have done what I hope it does!"

That said, I think the scenario you describe comes pretty close to what security you can achieve with reasonable effort. After all, even with a completely offline wallet you will have a similar risk exposure at the moment you decide to bring it back into a (connected) client to spend the Bitcoins in it---unless you are so diligent as to sign the transaction from an air-gapped PC not connected to the internet at all.

One problem I do see with your suggestion is that people are really good at tricking themselves. If I were to say "I'll only connect this PC to the internet when I spend these Bitcoins," I wonder if I'd live up to this promise. I suppose for me, the only way to protect me from myself was to set up the PC to indeed never connect to the internet. You may, of course, have more discipline than I trust myself with consistently living up to.