my file looks like this:
297 PC Closed 07/10/12 999000098 AMERICAN SOCIETY FOR HEALTHCAR 0.00 USD 1 NAI

i want to look line this:
297,PC,Closed,07/10/12,999000098,AMERICAN SOCIETY FOR HEALTHCAR,0.00,USD,1,NAI

Try this:
cat "File Name" | sed -e 's/ /,/g'

that's useless use of cat

With your command it replaces all the spaces with ",". which is not desired output.
see the output below..

$ echo "297 PC Closed 07/10/12 999000098 AMERICAN SOCIETY FOR HEALTHCAR 0.00 USD 1 NAI" | sed -e 's/ /,/g'
297,PC,Closed,07/10/12,999000098,AMERICAN,SOCIETY,FOR,HEALTHCAR,0.00,USD,1,NAI

5016487 RS Issued 08/22/12 7621 MOLECULAR DEVICES INC 4500.00 USD 1 NAI
5016488 RS Issued 08/23/12 7621 MOLECULAR DEVICES INC 2000.00 USD 1 NAI
5016490 RS Issued 09/04/12 22050 WUXI APPTEC, INC 3700.00 USD 1 NAI

Assuming you have similar pattern for all the inputs..

Try something this....

awk '{for (i=6;i<=(NF-4);i++){if(p){p=p" "$i}else{p=$i}}{print $1,$2,$3,$4,$5,p,$(NF-3),$(NF-2),$(NF-1),$NF;p=""}}' OFS=\, file