Upscaling is converting from a lower resolution (480, 720) to a higher one, 1080. It won't make a silk purse out of a sows ear, bit it may improve the picture somewhat. It will NOT be the equal of a Blu-ray disc.
Upconversion is taking a composite, possibly s-video, and component, to a format that has the possibility of a better picture, like HDMI. In and of itself, it doesn't affect the quality of the signal. It is simply a convenience to make connections easier.
FWIW, all HD televisions will take whatever signal is fed to them and internally "upscale" it into it's native format. IOW, you can feed it a component or composite signal and it will take it upon itself to do what it has to to provide you with the best possible picture.
Perhaps whatever DVD player you buy will have a better upscaler, but that's not a given. You may be better off simply letting the TV do it.