The JComments DB structure is same for J1.0 and J1.5... So if have J1.0 with JComments 1.4.0.9 and migrate to J1.5 and updage JComments to 2.0 all data will saved...
Iop!!! It's is as you'd said the structure of the database in both, Jcomments for joomla 1.0 - joomla 1.5, structure has such a similarity that you can import the table jos_jcomments from any version of jcomments in any joomla and the jcomments component will identified the comments.
So you know, i did as followed:
1- I stablish a new web site with J 1.5
2- Once Jcomments latest v was installed on J 1.5 y went to my previous database and copied the jos_jcomments table
3- on my new database it already host a jos_jcomments table, so i deleted that one (if somenone ones to keep it just in case, go ahead)
4- after I deleted the table on my new web site's database I droped the junk from my previous web site's database in it
5- and all the comments were transfer just fine
6- i watched my comments in my new site

lol
one thing tho, i was not able to combine both tables... in this case i did not need to, but if any one knows how to do it i'll appreciated
* Oh yeah, i forgot to mention that my previos website was J 1.0
Hope this info is usefull bye bye