Antec fans are designed to plug into the PSU molex connectors. I know. I have three Antec 900's.
If you look at your fan connectors, one side is a male molex, the other side female. I plugged the top and rear fans together and fed them from one PSU molex connector. Did the same with the two front fans.
Two of my systems are highly overclocked quads. With all of the fans set to Low, my load temps are below 70 C.
I also have the Atec 900 but i could never understand how anyone can stand the noise those three 120mm fans make if you care to cut your noise to over half and still keep the performance replace them with Antec's new true Quiet pro fans...the noise is like day & night its nice to have a watercooled computer which hardly makes any noise...Your fans noise level are up around 30 dba at high & these new fans at high are 18 dba and low 10 dba so what a difference in noise level..
I too just bought an Antec 900 case and am stumped with the fans. They are the 3 pin female connectors like in the picture posted by the op, my motherboard which is the asus m5a97 only has 4 pin headers. would i also need to buy the molex adapters to get it to work correctly ?
What i choose to do with my replacement Fans they can with an adapters 3 pin to 4 header..I read its better to go with the 4 pin and use a cord coming from you power supply...if you havnt bought your fans yeat consider using the Antec true quiet pro 120mm fan and it comes with the adapter you need plus it has a high & low speed switch which 90% of the fans out there dont have plus there super quiet..here is a Youtube link http://www.youtube.com/watch?v=nLq7mAisRRw