x10 mce remote questions. mapping and commands scope

[thl]

MediaPortal Version: 2.1.0
Windows Version: xp pro sp2
CPU Type: adm64 3200+
HDD: promise raid5, 3x200gb sata maxtor
Memory: 1.5gb
Motherboard: dfi lanparty 250gb nf3
Motherboard Chipset:
Motherboard Bios:
Video Card: nvidia 5200fx
Video Card Driver: latest whql
Sound Card:
Sound Card AC3:
Sound Card Driver:
1. TV Card:
1. TV Card Type:
1. TV Card Driver:
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec:
MPEG2 Audio Codec:
Satelite/CableTV Provider:
HTPC Case:
Cooling:
Power Supply:
Remote: x10 Sender OR23E Receiver CM23E
TV: epson tw10h
TV - HTPC Connection: vga

Hi,
I'd like to know if (how?) I can map a button on the remote (I think the start one is hardcoded and handled by the OS like the power one, so any other will be fine) so I can start mediaportal when I need it.
I'd like to limit the scope of the remote too, so it only controls mediaportal and not other apps (the pc is often used by my family members while I use mediaportal on the 2nd vga output and I don't want to send keystrokes to other apps).

thanks for the help

thl