Hi B2A2, unfortunately Janome software can't open or convert the ART format, however there is a free application by Tajima, I'm including the link to the website.
http://www.pulsemicro.com/ambassadordownload
Download it, install it and convert your designs from ART to Jef. Double check they will fit in the 140 mm x 200 mm or the 126 x 110 mm hoop. If they don't the program won't do the conversion.
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digimad