Remote Desktop/VNC to another computer

Wonder if someone can help. I have an iMac 2012 with Mountain Lion, and all have iPads and iPhone. So the problem I have is my Dad (old and new to computers!), is always asking about this and that jot working on his Windows laptop PC, and I have I try and explain, or more likely go around to do something simple.

So is there any simple software, or way for me to Remote Desktop him to help from home, either on my iMac, iPad or iPhone? As I say it will be from OS X ML, or iOS, to a Windows PC (running vista I think).

How will it work? I think Windows has Remote Desktop from windows to windows? But to be honest not sure how it works, if its secure etc?

Thanks

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I'm not bothered what system to be honest as long as it works, would be great if works over 3G as well on my iPhone!!

It's just the standard version of Vista, basic, I think he has. Also the less he has to do to "accept" etc the better, I want something where he doesn't have to initiate it ideally, as I say he's not at all tech savvy.

Thanks

Just had a look at teamviewer on App Store. So all you need to do is install teamviewer on the windows PC, register I take it with teamviewer to get a teamviewer ID.

Then on my iPhone type in the teamviewer ID and connect, over 3G or my own WiFi, and I have full control?

Can't be that easy, and its free? What do teamviewer get out of this. Does the computer being controlled have to accept the remote access?

Thanks