OK, about rhythm method. It's often used for contraception - the idea is to work out which days you're fertile on and avoid them. For us it's the other way round of course!
IIRC, you ovulate 14 days before the first day of your cycle (i.e. day one of your period). So you if you're regular you can have a pretty educated guess just by keeping track of your dates.
You can also find out when you ovulate by taking your temperature and also by looking at the consistency of your discharge (sorry if TMI!)
For the temperature, you need a special fertility thermometer - it's more sensitive than a normal one. If you ask your doctor I think they should give you one free, together with a chart for you to fill in. To find out when you ovulate, you take your "base temperature" every day. This the temperature before you get out of bed, so you start every day with a thermometer for 3 minutes. ("no I can't possibly take the DC to the toilet / let the cat out / make breakfast right now, it'll affect my base temperature 
")
You chart your temperature daily and you can see when you ovulate because your temperature dips slightly then rises (or it the other way round?! I forget, but it says on the charts anyway, and I'm sure 2 minutes on google would answer that one!)
I have to go out now (been waiting for a friend to get ready). I'll come back to the discharge TMI bit later!