An interesting thing happened on the way to ADO 2.0.  If you try to upgrade (or is it downgrade, really) your app from DAO 3.51 to ADO 2.0 with Jet 3.51 OLE DB provider, your application may fail if you try to access ISAM tables (dBase, Paradox, Jet 2, Fox Pro), Spreadsheets (Excel, Lotus 1-2-3), HTML files or Delimited and Fixed Text .  In addition, Jet 3.51 OLE DB Provider doesn't support linked tables.  So what can you do?  Upgrade to the latest ADO (2.5 at the time of the writing).  It ships with the Jet 4.0 provider, which supports all those things.  There is still one problem though.  You can read DBase and Paradox data, but you can't modify it unless you have Borland Database Engine installed.  Why?  Because MS & Borland did some type of deal involving 10% Microsoft investment in Borland, which removed those features from Jet & related technologies.  To read more on the changes in Jet, click here

So what's a developer to do?  We recommend the following. 

If your app accesses MDB data and/or various installable ISAMs, stick with Dao 3.51.  It screams past the latest ADO in this situation.  Seriously, I don't know how Microsoft can with a straight face recommend that everyone move to ADO, when it is horiffically slow against MDBs. 

If you are accessing corporate data residing in Oracle, SQL Server or Sybase, download ADO 2.5 - it is comparable to ODBC speeds.  If you are using Sybase, get their OLE DB provider.  It is ages faster than the ODBC driver.  If you are using Sybase Lite, you may have a problem here - their OLE DB provider requires Sybase Open Client product, which doesn't come with this version of the database.  If you have money to spare, I'd recommend getting the Merant (formerly Intersolv) OLE DB Provider for Sybase - it has no dependencies, but they charge you for it. 

Update (07-13-2000).  Visual Studio Service Pack 4 has come out and with it Microsoft brought back DBase and Paradox read/write support to DAO 3.6 and OLEDB 4.0 ISAM providers without having to buy any software from Borland.  Why did this happen?  The speculation is that Borland never liked that MS provided access to Borland data formats without having to buy associated tools (in this case Borland Database Engine, DBase and Paradox) thus obsoleting the tools.  After the investment deal, MS removed that support as a gesture to Borland.  Well, now Borland is porting its RAD tools (Delphi, Builder C++) to Linux.  MS obviously doesn't like that because having Delphi available for Linux means that hundreds of previously Windows-only Delphi shareware developers could port their wares to Linux with a simple recompile.  Thus, a retaliation, by restoring dBase & Paradox support.  I should say, that I have absolutely nothing to back up this story.  It is based purely on discussions in various newsgroups (which people in the know occasionally visit).