Are you sure your not just mis-interpreting megabits and megabytes
2.5 megabytes per second (+/- IP protocol packet overhead) is equivalent to 25 megabits per second.
Remember eight bits to the byte + 10% or so for the protocol overhead.
Given that both wired and wireless works, I can't think of anything else this could be, unless its some wierd NIC driver issue on the laptop.
Best way to test is to download a large file from somewhere on both machines at the same time. All things being equal, they should both finish the download at approx. the same time.