Couple unix commands

Hi ! I'm very noob and just started to learn unix. I have readed the manual but I still have many problems. Like, could you help me with these?

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1. How can I print users which are running some process, like pine? I just wan't to print usernames, and maybe that process name.
Am I even close? find -user -a | ps -a | grep pine   That gives error from that "-user -a" but prints something...
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2. How can I cut some text from these lines? Am I even close? grep FINDTHIS /user/file | cut ????

1:x:1078:FINDTHIS JEE, sometext, more
1:x:10523:FINDTHIS JEE, yeah, some again, something
4:xx:105233:FINDTHIS PLOM, plaaplaa, jeh
1:x:1078:FINDTHIS PLIM, foo, jeh
2:x:104:FINDTHIS FOO, fighter, foo, foo

So I have those lines in file, I wan't to cut ONLY text between ':' and ',' That should produce only these lines:

FINDTHIS JEE
FINDTHIS JEE
FINDTHIS PLOM
FINDTHIS PLIM
FINDTHIS FOO

How can I do it?
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3. How to print ALL system's useraccount names, and ONLY names, and ONLY each accountname ONCE? And that list should be in alphabetical order and reverse.

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4. How to count and print the number result for this? User's which are running some process, like pine, and count each user ONLY ONCE.

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5. I have large txt file. How can I print results which comes from only lines 50-60 and chars 10-15 from each line?




Thanks..

And I have done this--> rtfm... Still can't do those :) But almost.. Help?