Absolutely! The DVD should upscale your standard discs quite well depending on which one you choose - both the Tosh HDE1 and XE1 do this very well. You need to be aware though that these HD DVDs players will not play R1 discs but can handle any HD discs from UK/US plus all your R2 SD DVDs
A HD DVD player will upscale your existing DVDs to high definition resolutions - the idea is to select the resolution that matches your screen so there is no further scaling required. Whether the upscaled image looks better than from a non-upscaling image though depends on your screen - as the TV will scale everything to it's native resolution it's just a question of whether the scaler in the TV or HD DVD player is better. As Abbeygoo says the scaler in the Toshiba players is quite good so in most cases you will see an improvement.