Set WEP to 128-bit, replacing any cards that only offer 40 or 64l , then someone will have to spend at least an hour sniffing just to break the encryption, probably much longer since that figure is based on a higher-traffic office setting.
Even then if you have a software firewall running on your PC and keep your Microsoft patches up to date they'll only have access to network traffic, not to the files on your PC.
If you're concerned about neighbors instead of just drive-bys, change your keys once a week.
PS - even if they are sniffing packets, that won't let them get information out of packets when you're on a HTTPS secure page, since those packets are encrypted (using something much harder to crack than WEP) so that only the server you're connected to can decrypt them.