It looks like your HP PSC 2115 (PSC 2100 series) is supported under Linux: http://hpoj.sourceforge.net
I don't have any experience with Clark Connect, but in order to get the scanner working you need the hpoj software, and SANE installed. (http://www.sane-project.org
I just got my HP PSC 1210 working under Fedora Core 3, which was quite easy, but could not get the scan button to work neither:
'The "Scan", "Scan To", and "Start Scan" buttons on the front panel are not currently supported by the hpoj software. Always use the SANE frontend application to initiate scans.'
So I'm afraid it's not yet possible to get the button working under linux.
If you want to have access over the network to your scanner(from a windows machine), take a look at: http://sanetwain.ozuzo.net
hope it helps,