I had the idea of tweaking my laptop.

Specifically swapping the current WiFi card (Broadcom BCM4313) for an Intel Centrino Advanced-N 6230. Why? The drivers under Linux are hit-and-miss — nothing beats hardware that runs on the vanilla kernel. If I'd known it would cause so many problems I probably would have skipped the whole thing…

HP, it turns out, bakes a list of supported hardware into its BIOSes. If you install something that isn't on the list, turning on the laptop greets you with: 104-Unsupported wireless network device detected. System Halted. Remove device and restart system.

My own fault for not researching enough and assuming it would just work. Fortunately the card is compatible with my sister's laptop. I didn't waste any time and ordered an Intel Centrino Advanced-N 6200 instead — that one is definitely compatible. Finally Wepcrack won't crash on me in Linux and I'll get better WiFi signal.