Use the search button before you create a topic.
Anyway, you create an Infantry with a dummy weapon with Suicide=yes set.
Example:
[PARABOMB]
Primary=ParaExplosion
DeathWeapon=ParaBombDeath
;Dummy weapon
[ParaExplosion]
ROF=15
Damage=1
Range=255
Projectile=InvisibleAll
Speed=100
RevealOnFire=no
Warhead=PARAWH
OmniFire=yes
Suicide=yes
[PARAWH]
Verses=200%,200%,200%,150%,150%,150%,100%,100%,100 %,100%,0%
ProneDamage=300%
Sparky=no
InfDeath=2
Wall=yes
[ParaBombDeath]
Projectile=Invisible
Damage=300
Warhead=TerrorBombWH
Anim=RING1
Range=1.5
ROF=10
The Infantry unit also needs these tags:
Insignificant=yes
CanPassiveAquire=yes
CanRetaliate=yes
DetectDisguise=yes
DetectionDistance=255
GuardRange=255
OpportunityFire=yes
DefaultToGuardArea=yes
HasStupidGuardMode=false
AttackFriendlies=yes
AttackCursorOnFriendlies=yes
Explodes=yes
Selectable=no
PreventAttackMove=yes
Also, Download Deezire's INI editing guide. It will help with the tags.