How would I go about playing this?

It's meant to be for a server or something. A zip file: "sc4_creepsworld_v2" with a "svencoop" folder, that contains:

03/12/2013  01:15 PM    <DIR>          .
03/12/2013  01:15 PM    <DIR>          ..
28/10/2002  05:51 PM         2,466,104 deltar.wad
31/08/2010  05:29 PM    <DIR>          gfx
19/08/2002  12:48 AM         1,781,444 leprechaun.wad
31/08/2010  05:29 PM    <DIR>          maps
29/08/2002  03:56 PM         2,095,724 max.wad
31/08/2010  05:29 PM    <DIR>          models
03/12/2013  01:15 PM                 0 sc.txt
28/03/2003  04:25 AM             9,870 sc_creepsworld.txt
31/08/2010  05:29 PM    <DIR>          sound
12/01/2003  06:09 PM         5,006,992 tower.wad
30/12/2002  04:54 PM         2,320,584 Why1.wad
               7 File(s)     13,680,718 bytes
               6 Dir(s)   8,116,637,696 bytes free

Don't know if you can run Sven Co-op client-side only, but it's unlikely to work with anything that's not Half-Life.

Yeah, it's easy. Start a server on Zandronum, then select the option to play offline