most likely, although it wouldn't hurt to go with a 600W unit. with power supplies, there's a couple things to watch for: amperage across the 12V rail(s), efficiency, and brand name.
for the amperage, you'll want to see if the amperage on the 12V+ is at least 26A, but you'll preferably want it to be 35A or better. just keep in mind that most power supplies today have 2 12V rails, but some still only have one. it doesn't make that much of a difference between a single or duel rail PSU as long as the amperage rating is where it needs to be.
as for efficiency, you'll want to check that the power supply can run at 80% or better. the best way is to check and see if the power supply in question is 80-Plus certified. these units usually cost a bit more, but a highly efficient power supply is easier on the electric bill and have a longer life span which makes them well worth the extra money.
finally, you'll want to pick a good, reliable brand. Antec is a great choice, and i've been using Antec power supplies for the past several years. i've never had one fail (except for one case where the unit i had wasn't powerful enough for the system), and they do have a very solid reputation. other brands that tend to be very good in quality: Thermaltake, Rosewill, and Silverstone.
anyways, just follow those guidelines, and i'm sure you can find a solid power supply for the money.
as for everything else in your system, don't forget the operating system. since you mentioned DX10, i'm assuming that you'll be going with Windows Vista. just remember, if you want more than 3GB of RAM, you'll need to go with the 64-bit version of Vista so you can utilize all the RAM. if not, the 32-bit version will be just fine. also, unless your computer is on a network, Home Premium is the best choice for you. if you are on a network, and you need a lot of client-side networking options, then Vista Ultimate or Vista Business will be a better choice.
i'd also recommend that you invest in an X-Fi sound card from Creative Labs. the XtremeGamer version is an excellent value, and it will have a profound impact on audio quality in everything from games to music.
finally, don't forget the optical drive(s), too.
well, good luck, and if you need some more advice, just let us know.