I would buy another power supply.
Rule of thumb: If it's included or bundled...it sucks. Plus 350w in general will not be enough.
Take a look at the ANtec 430w or 550w. They would power the system no problem. Also make sure that you keep cooling in mind. As you know Athlons run hot. I would add in the cost of getting a better cooling fan than the stock crap that comes with it (i.e. you may want to get the chip oem rather then retail since I would recommend throwing the stock fan in the garbage)
Also get some case fans....great to buy a good system...but in a family that size, chances are it will be on A LOT! keep it cool....the antec power supplies can support multiple case fans with no problem. Can;t say the same for the 350w that comes with ut case.