Dunno if it's been covered or not, and I'm aware the thread may be finished/solved? But, your computers IP address is not your internet IP address (the one given to your residence by your ISP). Your internet/external IP address is registered to whoever is paying the bill, and that plus other personal info can't be obtained without access to your ISP's customer database (which is illegal and will put you in jail wherever you come from).
Your external IP address is sent out with every request (and some other packets) that your computer or other computers on your internal network make, to the internet. Wherever a request goes, your external IP address most likely goes with it. It's like a return mail address. You won't get what you asked for if you don't give a return address.
Your external IP address is also known as a public IP address. Your computer (in the home environment) will probably have a private address between 192.168.0.1 - 192.168.0.254 inclusive. Public addresses are used on the internet, private addresses are used within local networks. Public addresses connect different local networks/residences (simple analogy).
NAT (Network Address Translation) is what changes your computer's private address to the public address, within the packets (which happens at the modem/router, with ADSL)
Your computers MAC address is also sent with packets from your computer to whatever intermediary device it's connected to (router, switch), your MAC address never leaves on packets outside your local network. MAC addressing is used at a lower level than IP addressing, and isn't needed for internet communication outside of your LAN.
Ah gee, I'm on a roll. I really don't think you have an issue, providing you're relatively vigilant about internet use. Keep your security applications updated, protect your sensitive information/data.
Any public IP address can be learned, it just takes time, patience and piss-farting around, and the resources. No one wants to gain access to your home network anyway, there're bigger fish to fry.
Anyway, there are 2^32 IPv4 addresses minus private/reserved addresses, leaves 3,706,452,992 unique public IP addresses (under 32bit IPv4). Now that IPv6 has been rolling out, 2^128 gives the total number of unique IP addresses to be around 42 undecillion.
Didn't even mention subnetting. Mehh.