You have a few choices actually. The easiest would be to find an ATI x600 128 meg card. They made them to fit the M70 and Latitude D810. It's a drop in replacement. All you need to do is uninstall the nividia drivers and install the ATI drivers. The X600 can be had relatively cheap on ebay and would be the way to go if you want to ditch Nvidia.
Any of the GPUs that fit the Inspiron 9300 or M170 will also work but you'd have to swap heatsinks. The Nvidia cards for the 9300/M170 will run way too hot in your laptop so I'd stay away from them. It's a shame but the heatsink on the M70 is pathetically small.
There are 3 flavors of ATI x300 for the 9300 that will fit. One that's 32megs onboard but shares 32megs of system memory. A 64meg version that shares 64 megs of system memory and a 128 meg version (that doesn't share any system memory), this one would be preferred out of the three.
However, if you're looking to replace your Nvidia with another, you may want to look here http://cgi.ebay.com/DELL-NVIDIA-GO-1...item20b6fc7bf8
The only thing this guy sells is Dell laptop graphic cards. I don't know if he gets them refurbed from Dell or if he has the setup in-house to properly recondition / refurbish them. Either way he obviously doesn't bake them like others on eBay, or there's no way he could give a 60 day warranty. He's sold thousands of them over the last few years with a 100% rating and at $65 including shipping, you can't really go wrong. I would have bought this card myself, but the seller has banned me from buying from him and refuses to respond to my messages. (I made the mistake of asking him a while back if an ATI x1800 from an Inspiron 2010 would fit in a 9300 if I switched out the heatsinks.) He must have thought I was a flake or crazed modder. But I've kept him in my favorite sellers list in the hope that he gets another 7800GTX. When he does, he sells them cheaper than anyone else. Last time he had one for only $178, but I was in between paychecks and it sold hours after listing. The next one that pops up I'm having my mom buy for me (since I'm banned) before it gets away.
I hope this helps.