I had the hardest time figuring out how to import excel files that I actually just gave up and did it individually. I haven't really looked at import methods, but what I have been doing seems to work very easily for me. If you have all your boreholes in excel, open up the file you saved your work in and there should be a Microsoft Access file there. If you open that, it has all the headings you have on the borehole manager tabs (Location, lithology, stratigraphy, etc.) If you open the location tabs in Access, it will have the "excel spreadsheet" look. If you have your excel data look like the access file (leave a lot of the stuff blank), you can paste it in pretty easily. As long as you paste work in to match what the access file looks like, you should have no problem. I usually highlight the whole line when I paste.
You can do this for stratigraphy and lithology as well, just put a 0 or -1 if you want it to be in the legend and add your info in. It really becomes useful when you have tons of data. I had over 5000 data sets to put into the p-data and doing this allowed me to import it all in 30 min.....quite effective. Send me an email if you like this idea and can't get it to work, I can add screenshots.
Hope this helps