Checked the refurb page on apple.com, only $50 difference between refurb MacBook white CoreDuo 2.0GHz and refurb MacBook white Core
2Duo 1.83GHz, so seems like a no-brainer to get the Core2 Duo. I don't have a PC w/ Core2Duo but from reading tests seems the difference is worth $50.
One thing, I have 2GB DRAM in all my Macs. Recommend it, my MacBook runs much better than it did at 512MB. Bought at
www.memoryx.net, the cheaper non-OEM version, currently $109 per 1GB. If the $50 savings btwn CoreDuo and Core2Duo would make the diff btwn getting more memory or not, I'd go for the additional memory.