Should be easy, but its not, though probably not. Essentially what you are proposing is a portable computer designed to play games?. The DS and PSP and not computers, they are purposfully designed devices. Whilst a pc is multi purpose. Baring in mind the performance difference you also get with a big OS like Windows and then a smaller OS such as android. Your componenets will need to be a bit beefier.
Your best choise would probably be to use an Intel Atom based proccesor, then some discrete graphics(mabe a 300 series nvidia chip?). But then you have a mamoth task of cooling things. To make things easier i suggest using android, though i am not too familliar with the OS and not sure how it will perform 3d.
Im not sure on this but to reduce cost you could instead of using an Atom proccesor you could use a ARM Cortex or Snap Dragon processor(both are around 1ghz single cores). Though using android eliminates the posibility or using FPSC or DBPRO for game creation.
Another limiting factor is the control, i presume you are thinking of a handheld with buttons like the psp. The only way i can see DBPRO handeling thease is if the wired them up to a traditional keyboard so the button's reported difference scancodes/keystates.
Note, i have not proof read my post yet as im having to rush of to a lesson

I can count to banana...