There's no soldering involved. Just have to stick a screwdriver in that connector without stabbing yourself.You can do that hack or spend the moola to get the 360 HDMI kit. It's basically the same HDMI cable but a reduced profile AV adapter that fits in the slot at the same time. Like the cable hack shows, MS deliberately made the cables non interoperable. Considering you have to solder some connector and tear apart a perfectly good cable, I just bought the damn HDMI kit. Overpriced, yes.
Also note that this is the exact same adapter 360 Elite owners get in the box, so if you know a friend or look on Ebay you can get it cheaper.
Since Microsoft wants to grab all the money from their customers that they possibly can, they make the A/V cable incompatible with the HDMI cable in a couple ways. First, there's not enough space for them both to be plugged in at the same time unless you break off the plastic casing of the A/V connector.
Second, some models of the 360 will reboot continuously if both cables are plugged in, so you need to put scotch tape over the 6 pins in the bottom left of the A/V connector (on the narrower side of the connector.) Refer to this diagram but note that that diagram is mirrored as it is drawn from the perspective of the wires going into the connector. You need to cover up pins 20-30 on the bottom, which will be on the bottom left side of the part of the connector that goes into the 360.