Unknown Early 2000s Cheese Platformer

It would've been Vista; Windows 7 didn't come out until 2009

Doesn't seem like it. I've never even seen anything like MaidMarian before. The graphics are somewhat similar, but the visuals are far from what I remembered. The rat I remember was grey and fatter than the rat in Ratinator. The game itself was a 2D sidescroller (I guess you can say?), but it used sprites taken from frames of 3D animation... Either that, or there are actual 3D models in the game, but the camera is looking at it all like a regular 2D sidescroller. The game pack it (potentially) came from was more like a generic pack of Windows Vista games you could buy at Walmart at the time. Something similar to Hoyle Board Games, but I can assure you that this game more than likely didn't come from that.
HOWEVER. I do remember that around this time, I've seen or maybe even played Etch a Sketch (PC, 2008) around the time I saw this rat game. This is unlikely, but I feel like this game could've come from the same game pack as the rat game. Either that, or the games came from the same site if it was downloaded? The problem is though, I don't remember where this game even could've been downloaded. I remember it was a program similar to Steam, but it was way more appealing to older people who wanted to get games for their kids on the computer or something. It could've very likely been WildTangent Downloader, as I remember that we got Chicken Invaders from a download, and WildTangent was likely the only place you could get it that way at the time.