There are many ways to play an Am chord on the same instrument. I don't understand exactly what you want to know, but if the guitar tabs tells you to play an Am chord then that's going to sound good both on the guitar and on the keyboard.
Edit:
If you have a piece of tabulature that looks like this: (It's the first few notes of RHCP's Californication)
e------------------------------------------------------------
B--------0--1------------------------------------------------
G----------------------------0---2---------------------------
D-----2--------0--1------------------------------------------
A--0---------------------3-----------------------------------
E---------------------1--------------------------------------
You can use the pictures in bandcoach his post to find out what the notes are.
The first picture also says 'EBGDAE' like in the tabs. So the first number you see in the tabs reading from left to rights is 0.
This 0 is located on the A string. You can see in the first picture that at position 0 on the A string there is an A. (makes sense right?)
Next is the 2, positioned on the D string. You will see that 2 positions to the right on the D string there is an E.
You'll be able to find all the notes to play on the keyboard like this. It's very inconvinient but if you can only find tabs for a song
you really want to play on your keyboard this is how you do it.
I hope my explaination is understandable
