Hi Howard,
You won't get any of the upscaling benefits of the DVD player on your existing set, and it'll need to be connected via Scart/component (depending on your set's spec), rather than the higher-quality HDMI output.
All depends how soon you want to buy that flatscreen - if you're planning to buy pretty soon, you could buy the player now and enjoy it on your existing set (a good DVD player should work well however you output its signal) in the meantime.
However, if you're not planning a set upgrade for some time, I wouldn't invest a lot of money in a feature-crammed player now, as they (and their HD DVD and Blu-ray offspring) are getting better-value all the time: your budget today will buy you a superior product in six months time, let alone a year.