Good luck hitthepin, I hope we both enjoy a good game.
Chess on an Infinite Plane (hitthepin - captaintugwash)

If its infinite, couldn't one of the kings run away forever, dodging any checkmate since the other side has limited peices and can't cover all files or diagonals???

No. It's pretty easy to imagine a checkmate with three rooks vs a king on an open board. Considering we have five pieces that have rook power (at least), and 24 pawns, I don't anticipate a problem winning against someone whose strategy is to run away. The king can take a million moves if it wants to run far away, but the rook takes just one move to overtake it and stop it advancing further. Then the other rook, then the queen... no problem.

This thread is a game of "Chess on an Infinite Plane" between hitthepin and captaintugwash.
Rules:
The Pieces:
Black and White each have the following pieces (quantity and name):
1 king
1 queen
2 chancellors
2 rooks
2 bishops
2 knights
2 guards
2 hawks
24 pawns
All pieces move as in classical chess, with the "extra" three pieces moving as follows:
Chancellor (C) - Moves and captures as rook + knight.
Hawk (H) - Leaps exactly 2 or 3 squares in any orthogonal or diagonal direction. The leaping move means it can jump over other pieces.
Guard (G) - Moves and captures the same as a king but is not affected by check.
Pawns play the same and promote at the same rank as in classical chess. White pawns promote at rank 8, and black pawns promote at rank 1. Pawns can promote to chancellor, hawk, or guard in addition to queen, rook, bishop, or knight. Pawns may capture and be captured en passant with the same rules as in classical chess.
Board Setup:

A red bracket indicates the a1 (1,1) square.
There is no castling.
There is no fifty-move rule. Draws can only occur from stalemate, threefold repetition, agreement, or a proven case of insufficient material to force checkmate.
All other rules are the same as in classical chess.
Move Notation:
Numeric coordinates are used to identify piece locations as (file#, rank#). Parenthesis are used around each coordinate. Three examples of a move notation:
1) A rook moving from (8,4) to (1,4):
R(8,4)-(1,4) or R(1,4)
2) A rook moving from (1,4) and capturing a piece on (0,4):
R(1,4)x(0,4) or Rx(0,4)
3) A pawn advancing from (-1,7) to (-1,6):
(-1,7)-(-1,6) or (-1,6)
hitthepin plays White. Good luck to both players!