You don't say good-bye to Dell warranty if you upgrade the RAM on your own. There is no sticker or anything for them to find out about your tinkering. I've paid additional 6k for 3-years warranty and trashed the original 512MB stick on day 1. However, I've it with me, just in case, when Dell rep. comes to fix the system and are very particular about it, I can swap
And yes, a single 1GB 667MHz laptop RAM from Transcend costs 2.2k only.