Dell laptop with DisplayPort (but NOT mini) to Thunderbolt monitor I have a DELL E6410, with DisplayPort output. How can I connect it to an Apple monitor with a Thunderbolt input? Searching for that kind of adapter keeps returning mini DisplayPort ones, which won't help.

Going through DVI or HDMI perhaps?
According to Apple's spec page, the Thunderbolt Display requires a Thunderbolt-equipped Mac. So, I don't think there is any way to get it to work. Although Thunderbolt allows for video steams and you can connect a DisplayPort monitor to a Thunderbolt port, the reverse is not true.

If you can get your hands on the older Apple Cinema Display with a mini-DisplayPort, that should work with something like this.