Serial Read at any point in a program?

I think I know the answer to this, but I thought I would pose it anyways in case you programming gurus have any ideas.

I have a program that is reading temperature sensor data and logging it to a spreadsheet. I got this working.

Now I'm trying to add some functionality where a command is sent over serial and read by the Arduino to go do something.(Change position of a servo motor). I got this working. haha

But what I would like to happen is that if the Arduino gets a command over serial, stop what its doing... change the servo position... then continue on with the program where it left off.

The reason is I am recording 120 temp readings over a 5 minute period which is one time through my main loop. I don't want to have to wait 5 minutes for the program to get to the point where it reads the serial command. I want it to execute the serial command as soon as it receives it.

My gut feeling is this is not possible. The only thing I was thinking was putting "check for serial command"s at various places in my code so it checks every few seconds instead of every 5 minutes.

Any guidance would be appreciated.

Probably, the 'blink without delay' example sketch in the IDE will help you, but without seeing your code I can't be sure. My crystal ball running XP has crashed!