Hmm, for an extra $10 or so you can get a 20" Acer widescreen which has 1680x1050 ability vs the 1440x900 of the Hans-G.
I like the Cent 534 better than the 5, and it's the same price... I guess it's just personal preference.
If you want to save a little money you could go with G.Skill DDR2 800 RAM 2x 1GB for $85, not sure how crucial it is for your brother to have the CAS 4 timings.
Other than that not sure why the mouse has to cost so much but I guess everyone has things they like (= I prefer less expensive mice/keyboards (and with cords) that way I don't have to invest in batteries, and also can use money saved to get better overall parts (things that will affect performance like cpu/gpu).
Other than that though the build looks good. I'd recommend a bigger PSU, but that's just because it would allow for upgrading in the future (without replacing PSU), not really a necessary change.
I run those in an Asus motherboard with a 65W Athlon X2 4200+, as a HTPC.
Do that, and then you can get a bigger HD. Either the Seagate 7200.10 400GB or one of the cheaper 500GBs. I always advise more HD space than you think you need. I have 1.1TB right now, with only 410GB free. Previous PC only had 240GB total. So, in the span of a couple months the amount of saved data I have grew from about 180GB to 690GB. New games are averaging, what, 7GB? Yea, what were they 2-4 years ago? I wouldn't be surprised to see some 15-20GB games coming out in 2 years, I won't guess on 4 years.