Win7 nowadays supports adding tags to files, and sorting/displaying files according to tags. However, only documents created by Office or image files support adding tags, while my favorite tag-arranged files are pdfs and archives (zip, rar, iso, etc). So this nested functionality of win7 can not satisfy me. Meanwhile, TotalCommander can add comments to files, but this functionality is insignificant, because these comments are stored in a separated file, which means if the target file is copied/moved to another place, comments will be lost.
Today I find this longing functionality in Xplorer2, which only works under NTFS format. Firstly you can add comments(here I use it as tags) to any kinds of files by selecting this file and [Action->Set comments]. Then you can search or select files with a particular tag as follow:
Open the find files window: ctrl+f;
Add a new rule in the “Additional Rules” frame;
In “Rule definition” panel, select “Comment” from “Property & description” drop-down list, and specify the tags in the textbox beneath “Text Settings”;
Bingo!
For more details see "Attaching comments to selected items" of Xplorer2's documents.