According to the MS Technet web-site (http://technet2.microsoft.com/Office/en-us/library/6a13cd9f-4b44-40d6-85aa-c70a8e5c34fe1033.mspx?mfr=true), there is no hard limit in the 2007 version. However, there are effective limits beyond which performance begins to suffer. Here are those limits:
Column
2000 per document library
4096 per list
This is not a hard limit, but you might experience library and list view performance degradation as the number of columns in a document library or list increases.
