Bob: That should work out to about $15 per month from now until 2020. You can do it. By then the prices on UMPC should drop a bit and have improved functionality.
OK, it can read A4 and letter sized PDFs.
Now the question on everyone's mind is: "Can you keep the Lenovo X61 working for 13 years?" Or are you going to use Paris Hilton accounting and get a new machine later this year?