First off, if any of you are familiar with the PS3 XP lobbies, it works the same way. First go to your MW3 game location and the player 2 folder, mine is "C:\Program Files (x86)\Steam\steamapps\common\call of duty modern warfare 3\players2". Next open config_mp.cfg with notepad ++ or regular notepad. now add this to the file at the end:
YOU MUST BE HOST FOR THIS TO WORK!!!!!
seta scr_ctf_score_assist "10000"
seta scr_ctf_score_kill "10000"
seta scr_ctf_score_suicide "10000"
seta scr_dem_score_assist "10000"
seta scr_dem_score_kill "10000"
seta scr_dem_score_kill "10000"
seta scr_dem_score_suicide "10000"
seta scr_dm_score_assist "50000"
seta scr_dm_score_kill "50000"
seta scr_dm_score_suicide "50000"
seta scr_dom_score_assist "30000"
seta scr_dom_score_kill "30000"
seta scr_dom_score_suicide "30000"
seta scr_ffa_score_kill "30000"
seta scr_kc_score_kill "30000"
seta scr_koth_score_assist "30000"
seta scr_koth_score_kill "30000"
seta scr_koth_score_suicide "30000"
seta scr_sab_score_assist "30000"
seta scr_sab_score_kill "30000"
seta scr_sab_score_suicide "30000"
seta scr_sd_score_assist "30000"
seta scr_sd_score_kill "30000"
seta scr_sd_score_suicide "30000"
seta scr_tdm_score_assist "30000"
seta scr_tdm_score_kill "30000"
seta scr_tdm_score_suicide "30000"
seta scr_war_score_assist "30000"
seta scr_war_score_kill "30000"
seta scr_war_score_suicide "30000"
You can change the amount of XP by changing the numbers in quotes
The Max XP per kill is 65,000 if a player gets more, they will be kicked by the game
For the XP to keep the host must leave before the other players do
Have fun