I don't see any place to set mtu on a 2524, and I seriously doubt that is your problem. WinXP's default mtu is 1500; if XP can talk at all over this link then it is passing 1500.
What errors are you getting on the 2626?
Oh and yes, your switches are compatible as shipped from the factory. You can change enough of either one's config to render them incompatible.
--
The stagehand's axiom: "Never lift what you can drag, never drag what you can roll, never roll what you can leave.