You cannot use download feature with ARC250 software. At one time Butel had a Web Service Utility which would download trunking systems in csv format, but I can't locate the program in either RRWiki or Butel's homepage, so it may be not be available anymore. I have and use it occasionally, but Win96/97 will download conventional as well and its normally easier to copy/paste from them.
ARC250 does have a feature for importing trunking or conventional frequencies using the ADI (Advance Data Import) Icon.
To use, open a webpage and highlight and copy a group of frequencies then click the ADI in ARC250. This opens an import dialog, click the import from Clipboard then hit the All button then click Export to Table if you desire the frequencies in the open ARC bank. Or click Export to clipboard if you are building a file in a spread sheet such as excel.
BTW, if you have excel you can also highlight and select copy, a section of TG's and Tags from a RR page and paste into excel by right clicking in a field (A1 for example) then select Paste Special and the text option. This will allow easy editing to structure data for copy and paste into the TG part of ARC.
Alas . it would be much nicer if the software had full Web Import like the 246/396/996.
Edit: BTW, in ARC, clicking the (?) Help will bring up a menu which has ADI listed first. This may provide a better description of using the feature.