The CPU will only determine how fast queries are processed. The number of concurrent users will be dependent on system memory. If each apache query uses approximately 20MB, you can accommodate approximately 100 concurrent users, assuming all memory is available to apache. If you have mysql running as well, you need to consider that in your memory needs.
The uplink speed typically determines your burst capabilities. If you were on a 10mb port, you would be limited to a speed of about 1.25Mb/sec. On a 100mb port, this would increase to 12.50Mb/sec. If you don't expect to push much bandwidth, then I wouldn't worry about the uplink speed so much.
Have to agree with the recommendations for a more powerful processor. Even if you're able to accomodate the current requirements, I really think you'd see significant improvements in performance with a better processor.
From Intel's site: The Intel Atom processor was purpose-built for simple, affordable, netbooks and nettops.
Do you want to trust (critical) server apps to a simple netbook processor?