CARGO LTT DSNDING TO 9000 FT; FLEW AT 300 KTS BELOW 10000 FT AND OVERSHOT ASSIGNED ALT BY 700 FT; GETTING AS LOW AS 8300 FT. A CONFLICT OCCURRED WITH A COMMUTER DASH 8 THAT THEY OVERTOOK AND PASSED.

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THE FOLLOWING CIRCUMSTANCES RESULTED IN A LOSS OF SEPARATION AS ADVISED BY CANADIAN ATC DURING A DSCNT INTO THE TCA OF CYVR. I AM A RECENTLY UPGRADED CAPT FLYING CARGO-ONLY; LIGHT JET ACFT ON AN EXTREMELY LABOR INTENSIVE; SHORT FLT FROM BFI TO CYVR. THE RTE CONSISTS OF A SID TERMINATING AT AN ARR STAR WHICH DEMANDS A GREAT DEAL OF CONCENTRATING FROM BOTH PLTS. AS PNF; I WAS CONCERNED WITH SETTING UP APPROPRIATE NAVAIDS; PERFORMING CHKLISTS; AND ATTAINING THE CURRENT ARR ATIS. WE WERE CLRED FROM FL200 TO DSND TO 9000 FT. AS WE APCHED 10000 FT I NOTED THE COPLT'S HIGH AIRSPD OF 300 KIAS AND ADVISED 'AIRSPD; 1000 FT TO GO.' HE ACKNOWLEDGED BY DEPLOYING THE AIR BRAKES TO SLOW HIS AIRSPD. I THEN WENT BACK TO SETTING THE NAVS TO THE NEXT SEGMENT OF THE ARR. MY NEXT GLANCE AT THE INSTS INDICATED AN ALT SLIGHTLY BELOW 8800 FT. I APPLIED MAX PWR WITH THE THROTTLES AND THE PLANE LEVELED AGAIN AT 9000 FT. ATC PROMPTED US ABOUT OUR ALT SIMULTANEOUSLY. UPON LNDG WE WERE INFORMED THAT A LOSS OF SEPARATION HAD OCCURRED WITH A COMMUTER DASH 8 WHICH WE HAD OVERTAKEN FROM ABOVE; PASSED; AND SUBSEQUENTLY DSNDED IN FRONT OF. ATC FURTHER ADVISED US THAT HE HAD SEEN US AS LOW AS 8300 FT; AND HAD ALSO TEMPORARILY LOST OUR XPONDER. NEITHER MY FO NOR I TOUCHED OUR XPONDER. MY QUESTIONS REGARDING THE INCIDENT TURN TO THE DIFFERENCES BTWN UNITED STATES AND CANADIAN ATC ALT ALERTING SYS AS WELL AS THE SYS ABILITY TO KEEP UP WITH ACFT IN CLBS/DSCNTS. IN HINDSIGHT; I WILL DOUBT MY COPLTS MORE OFTEN. MY FO HAS TWICE MY FLT TIME AS WELL AS JET AND TURBOPROP EXPERIENCE; EXPERIENCE FOR WHICH HE HAD SPECIFICALLY BEEN PAIRED TO ME. I ERRED IN MY OVERCONFIDENCE IN HIM. SECONDLY; IT SEEMS WISE IN FUTURE FLTS TO NEVER TURN MY ATTN TO ANOTHER TASK DURING THE FINAL 1000 FT PRIOR TO ANY LEVELOFF.