One please dont cus on this site.
Two Why do you think the guppies killed your fish?
Three neons are harder to take care of than the guppies and require different water conditions than the guppies.
Neons like softer water.
"They do best in temperatures of approximately 78 degrees Fahrenheit and pH levels between 6 to 6.5. Neons prefer to school in the middle range of the tank. Neon tetras are sensitive to water quality. Since water quality in beginner aquariums may be suspect they may not be the best choice for absolute beginners"
http://www.centralpets.com/pages/critterpa...h/FWF4630.shtml