the days of the hardy guppies are nearly all but over. new strains have been weakened through inbreeding, and it can at times be hard to produce viable fry. however, that is not to say it cannot be done. i used to breed guppies, producing about 50 good fish a year. but soon i gave up on the idea of guppy breeding, as it was hard to find people to take the young off my hands due to the reputation guppies were beginning to pick up. so i gave up on guppies, and allowed my stock to decline until there were none.
recently though i have revived my passion for guppies, and have set up a 4gal planted tank with a 12 volt halogen light, and plants including 3 young amazon swords, an unknown sword, parrots feather, bronze bacopa and some crypts. it has a sand substrate and an open ended airline providing air. instead of a filter i am carrying out water changes of about 50% every 6 or so days. i keep the tank at room temperature.
i had stocked it with 4 female guppies (which i have found to become very colourful these days) and a male. they are all very beautiful fish, but sadly i have lost one of the females. all the others seem very healthy though, and so i guess that it was just one of those things. two of the females are now looking very pregnant, so i egarly await the arrival of some fry. so in conclusion i would fully recommend you go ahead with guppies. they are still a lovely fish with plenty to offer to the hobby, the only difference is now you cannot neglect them, which really shouldnt be done anyway. keep on top of maintance, and they will certainly bring you lots of joy. good luck!
(pictures of my 4gal guppy tank can be seen on the link below...)