I recommend everyone takes a browse of www.gtagaming.com's download areas for GTAIV - quite a few interesting tools and mods have begun to emerge.. many to facilitate further modding... by the likes of us, I'd suggest.
Enjoy.. I know I did.. it's got me thinking.
And while I'm at it, really I should give full credit to where I stumbled upon news of these mods - one of our own resources, through which I was browsing many neighbourhoods in the GTA scene.. http://planet.drugcrew.com - from here you can browse news blogs and forums posts from every corner of the GTA universe - all with the latest Web 2.0 tek.