Yes, open your Hammer-->go to options--> Textures--->add wad--->Decals.wad.
Once decals.wad is in your hammer.. Create an 'infodecal' (Hammer Entity)
Select the entity and view it's properties.
Click 'texture' And when you go to choose the texture press { to filter the decals.. look for a '{blood3'.. (or something)
Once you've selected the decal that you want, give the entity a name..
'decal1'..
now once triggered the decal will appear.. so trigger it as soon as he lands.
Relize that in order for the decal to work it must be directly on the floor..
to easily do this.. click the infodecal entity from the list and then click in the 3D view window.. this will put it direct on the floor, or wall.
Check out this cool example bsp I made.. When the grunt lands on the pipe.. blood sprays up in the air.. I then triggered a infodecal to put blood on the overhead lights.
http://twhl.co.za/mapvault_map.php?id=2624Anyway's hoped this helped.