most consumer Video DVDs are either 720x480 or 720x576
Like I said, basically 640x480. Ever-so-slightly more if you're running PAL. If 720x576 upscaled on an HDTV is watchable, 640x480 upscaled on a 24" monitor won't look bad either.
there's also a big difference between movie upscaling & video game upscaling since in a video game you may have more static images which are more prone to showing lack of details
What's that got to do with upscaling? If your game is lacking in details, it's lacking in details. Upscaling will neither fix nor aggravate this.
not even considering the difference in upscale algorithms
PC video cards use state-of-the-art upscaling algorithms. If you can be satisfied with results from a HDTV's upscaler, you can be satisfied with results from a PC video card upscaler.