The adif2dxq program converts ADIF contest logs from N1MM, Win-Test and WriteLog (and possibly others) into DX4WIN .DXQ format.
Version 5.23 of the program was released on 10 April 2012. Click on this link to download the program. Click on this link to see the version history.
There is nothing wrong with importing a contest ADIF file directly into DX4WIN. For many, this is a perfectly acceptable solution. However, the adif2dxq program offers a few features beyond simple ADIF import:
To install the program, extract the adif2dxq.exe file from the .ZIP file, and save it to your DX4W### directory.
To run the program, navigate to your DX4W### directory and double-click on the adif2dxq program icon. The program will look something like this:

Specify the ADIF input file by clicking on the ADIF button. Once you specify the input file, the output file will be given the same name, but with a .DXQ extension. To change the output file name, click on the DX4WIN button.
Next, select the Format for the .DXQ (output) file. If you are using DX4WIN 8.0x, use the default format (DX4WIN8). If you are using DX4WIN 6.0x or 7.0x, choose the DX4WIN6 format instead. You must select this same format when importing the .DXQ file into DX4WIN (see below).
Next, select the Contest type. Not all contests are supported, others may be added over time. The operation of the program is unpredictable if you select the wrong contest type for your log.
Enter a Group Number, if desired. The default is Group 0 (the "all QSOs" group). Remember that you can also set the group number in your DX4WIN preferences, before starting the import.
You can enter text in the QSO Note field. You can put any text there you want, up to a maximum of 64 characters.
There are four optional checkboxes:
Finally, click on the Convert button to perform the conversion. If there are any warnings, they will show up in the window.
To import the resulting .DXQ file, choose File | Import/Export from the main DX4WIN menu. If you are using DX4WIN 8.0x, select the line in the Import/Export Filters window with DX4WIN8 in the ID column. If you are using DX4WIN 6.0x or 7.0x, select the line in the Import/Export Filters window with DX4WIN6 in the ID column. This must match the Format you chose when you converted the ADIF file. Next, in this same window, choose File | Import, then navigate to the location of the .DXQ file. Click on the name of the file, then on the Open button. DX4WIN will bring up an "Options for duplicate QSOs" window. Choose "Issue warning and stop". Then click on the OK button to import the file.
(new contests in bold)
(*) This is a special case of the program that does not populate the Recvd field in the logbook. It can be used to add an optional QSO Note and/or Group Number to each QSO in the ADIF file before importing it into DX4WIN. It recognizes these ADIF fields: GRIDSQUARE, NAME, NOTES and QTH. Others can be added upon request.
This program is offered as-is. I'll try to support it as best I can, but development is primarily motivated by the contests I operate.
I've only tested with very recent versions of N1MM, Win-Test (limited) and WriteLog. If the conversion doesn't go the way you expect, send me the .ADI file and I'll try to fix it.
If there is a bug, please let me know. If you want me to add a particular contest, the easiest way is to send me the .ADI (ADIF) file from your contest logging program (and of course tell me which contest it's from).