You can buy the Chaintech VNF3-250 for 54 bucks shipped at zipzoomfly.com.
At newegg, the buyers gave it the same 4/5 egg rating as the Epox EP-8KDA3J.
IMHO the quality of MSI boards has gone down over the last few years and Biostar's support of their boards is less than stellar.
The latest V6.0 BIOS for the VNF3-250 doesn't include Vcore adjustments, but if you buy a Sempron with the E6 stepping (or even possibly the E3 stepping), you likely won't need that feature since the E6-based Semprons will generally clock to a minumum of 2 GHz at stock Vcore. For the VNF3-250 I recommend a single 512MB stick of PC3200 DDR, Win2K or later and the addition of a fan to the heatsink mounted on the nf3 chip. For maximum safety you might want to add a USB2 card and use that exclusively for USB since many of the problems with the VNF3-250 reported in the newegg reviews seem to originate from the on-board USB.
You won't need any special cooling for the processor - even overclocked the retail fan will suffice (recommend reasonably ventilated case). It won't get hot and it won't be loud, even at 2+GHz.
On my VNF3-250 board (1+ years old) my Sempy 2500+/E6 (1.4GHz stock), retail HS/fan, has achieved 2.2GHz at default Vcore (haven't tested it w/ PRIM95 at that speed however). For a mild and virtually guaranteed stable overclock for your parents, I recommend a BIOS setting of 250MHz CPU / 3X HT / 166MHz memory (for the VNF3-250 V6.0 BIOS which reverts 4X HT to 3X at 250MHz anyway). With the Sempron 2500+ these settings result in 1750 MHz; using the Sempron 2800+ it yields 2 GHz with memory theoretically overclocked by 4 percent in both cases (on my board running under the V6.0 BIOS, CPU-Z reports memory speed of 194.4MHz/388.8DDR at the settings described above so I run mine at 257 / 3X / 166 to obtain essentially 1.8GHz [7 x 257] with memory reported by CPU-Z as 200.2/400.4MHzDDR).
Either of the two processors mentioned above, clocked in the manner above will give your folks plenty of spare CPU cycles to burn. If they aren't gaming fanatics.....