There are three steps to install the GarSim GNS530 hardware.

1. We have to map the buttons on the GNS530 to key presses in FSUIPC4
2. We have to modify the RXP.INI file to map the key presses to the software functions of the Reality XP gauge.
3. We have to modify the panel.cfg file for each aircraft to hide the border and size the gauge to fit on the LCD display.


Firstly modify, FSUIPC4.INI (valid also for Win7)

In order to map the keys you will need a registered copy of FSUIPC from Pete Dowson. 
Input Assignments-
Copy and paste the buttons section below into your FSUIPC4.INI file to define the button presses.
The number after the P or the R in the below example is "0"
Change this letter "0" to correspond with the correct joystick number that is recognised in FSUIPC, this will depend on how many devices you have already attached.
To find out the joystick number, plug the GNS530 into the USB port and start FS.  from the Add-ons menu select FSUIPC and then go to the button/keys tab.  Pressing any key on the GNS30 will show you which joystick number is assigned. 

The file is usually located here:-

C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\Modules

FSUIPC4.INI

[Buttons]
ButtonRepeat=20,10
1=P0,12,K81,40
2=P0,0,K83,40
3=P0,1,K83,40
4=P0,13,K87,40
5=P0,2,K89,40
6=P0,3,K90,40
7=P0,7,K75,40
8=P0,6,K74,40
9=P0,5,K118,40
10=P0,4,K117,40
11=P0,14,K78,40
12=P0,16,K120,40
13=P0,17,K86,40
14=P0,18,K124,40
15=P0,19,K65,40
16=P0,20,K67,40
17=P0,21,K113,40
18=P0,10,K119,40
19=P0,11,K79,40
20=P0,8,K123,40
21=P0,9,K121,40
22=P0,15,K122,40
23=R0,27,K72,40
24=R0,26,K73,40
25=P0,25,K114,40
26=P0,24,K115,40
27=R0,23,K116,40
28=P0,22,K125,40
29=P0,29,K126,40


Secondly modify, RXPGNS.INI (valid also for Win7)

Each button press or encoder click is recognised by windows game controller software as a joystick button input from the GNS530.
The Reality XP software must be configured to recognize these key strokes and mapped to the various functions of the software. This is assigned in the RXP.INI file. 
In the [KEYBOARD] section of the ini file, the keys for the 530 should be as below.  Copy and paste over the top of the original keys which are not defined.

The file is usually located here:-

C:\Documents and Settings\All Users\Application Data\Reality XP\Common\Settings

530_CONTRAST_INC=win+y
530_CONTRAST_DEC=win+z
530_CONTRAST_RESET=
530_POW=win+s
530_COMFLIP=win+q
530_NAVFLIP=win+w
530_CDI=win+F9
530_OBS=win+v
530_MSG=win+F13
530_FPL=win+a
530_PROC=win+F2
530_NAV=win+c
530_DTO=win+F3
530_MNU=win+F4
530_CLR=win+F5
530_ENT=win+F14
530_RANGE_INC=win+h
530_RANGE_DEC=win+i
530_LKNOBO_L=win+j
530_LKNOBO_R=win+k
530_LKNOBI_L=win+F6
530_LKNOBI_R=win+F7
530_LKNOBPUSH=win+n
530_RKNOBO_L=win+o
530_RKNOBO_R=win+F8
530_RKNOBI_L=win+F10
530_RKNOBI_R=win+F12
530_RKNOBPUSH=win+F11
530_EXPORTFPL=
530_SWAPRADIOS=win+F15



Finally, modify the Panel.cfg 

Select an aircraft which has the Reality XP GNS530 gauge installed (using the reality XP config tool).
Next, we have to make a small modification to the panel.cfg file for the aircraft. This has to be done for the panel.cfg file of every aircraft you wish to fly with this software/hardware.
The below example is for the Microsoft Cessna 172 located here for FSX-

C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\C172\panel

copy and paste the line shown below over the top of the existing line entry.  This will re-size and crop the gauge to fit on the LCD screen.
The important part is the -29,-12,155,150 which defines the size of the gauge.

panel.cfg

gauge00=rxpGNS!GNS530,-29,-12,155,150