Anything Asus is great motherboard wise and as far as a cpu goes I would go with an i3.
Agreed. Considering he's got a Sempron now though, dropping back to a Pentium (e.g. 860G) to save money is still going to be a great choice for him.
If Asus is a little pricey, check out ASRock. I don't trust MSI for mobos, especially at the low end. They use weak VRMS, which may pop under load. There's a public reference spreadsheet I can't link at work, but trust me it's got at least half a page of problematic MSI boards on it.
The PSU is
a big deal though, since the entire system is dependent on clean, reliable power. The cheapest PSU I could recommend is the Antec VP-450, which is efficient enough for 80+ but is disqualified for not having active PFC. The 380W Antec Earthwatts is another good choice, as is the 360W Seasonic 360G.
A cheap PSU-shaped object pre-installed in a case is probably junk to be avoided. Raidmax, Apevia, Logisys, Xion, Diablotek, and CM (Coolermaster) are examples in this category.