If you are unable to find a sport-science lab to find out your max HR and lactate threshold, then you find out by "perceived effort".

A good way to find out your max HR is to find a flat stretch of road and pedal as hard as you can - every time you get on top of a gear, move into a harder one... your HR will begin to climb. The other way is to climb up a hill - not a steady rate, but again, trying to get on top of a bigger and bigger gear.

At the point where you begin to feel sick (as - oh no, I think I'm going to vomit) you have almost reached your max and you can use the highest HR you got to as your max.

Your LT - which is something you will see talked about a bit here too (like Cassandra's post) is also relatively easy to work out by perception.

You know the point where your legs start to ache... maybe you are climbing up a hill, and just want to make it to the top and you put in a little bit more effort to make it there... and your legs are saying "naff off, we do NOT want to do this"... thats when you glance at your HR monitor and that HR will be approx your lactate threshold.

This will be confirmed as you get over the hill and it takes a while (sometimes 5-10 minutes) for your legs (specifically thighs) to feel normal and able to work again properly.

Perceived effort/exersion is a good way to work out some training zones for yourself.

The Female Cyclist or The Cylists Training Bible are two good books that explain this in more depth