Do you mean like /usr/bin/top ? If you want to look at a particular process, you could use 'ps' for that.
If you want to keep an eye on a particular process but want to narrow it down a little, you could use /usr/bin/watch and /bin/ps like this:
watch -n 1 "ps waux | grep processname"
Go ahead and play with that a bit. The -n switch specifies how often the watch program refreshes the display. Also, you may or may not need a - in front of the waux. I dunno.