First, you can't openly purchase notebook motherboards. There is no retailer that sells motherboards for notebooks.
Second, the Pentium M is Socket 479, not Socket 478.
Third, the Pentium M (Banias and Dothan) has a different pin layout than the Core Solo/Duo (Yonah). They're both Socket 479, but the Yonah has a different pin layout, meaning some pins are placed in different places. This means that you're unable to buy any of the Core Solo or Duo processors and just simply swap it out with your Pentium M. You'll just have to upgrade to a faster Pentium M.
Bahawolf, Newegg.com mislabled that processor. All of Intel's current mobile processors (Banias, Dothan and Yonah) are Socket 479. The only one that won't is Intel's next-generation mobile processor, code-named Merom.