DNS allows you to point pretty much anything to different servers/ip 
addresses/etc (ie have mail go to one location, www.domain.tld go to 
another, ftp.domain.tld go to another) but as already mentioned, this 
needs to be configured by whoever controls the DNS server (# whois 
domain.tld --- look at the Domain servers list).

If you or your client has control over the registrar of the domain name 
(ie can go in and specify new DNS servers) -- you could use a free DNS 
service such as zoneedit.com and then have full control over the DNS record.

After the DNS is pointed to ISPB, the problem will reside with ISPB. 
Most likely your ISPB account is named based -- many different domains 
share the same IP address. It is very common in shared hosting 
environments. As a result, the web server configuration will need to be 
updated to know how to handle the new domain. At some web hosts (such as 
those that use the CPanel interface) account holders can "park" a domain 
on top of a subdomain and it will automatically update the server 
configuration (httpd.conf). Other hosts will do this as a support item 
and others may simply refuse.

My advise --> If the client is an actual business/company/etc put them 
on their own account. Web hosting is cheap in the grand-scheme of things 
and the few bucks that might be saved are not going to be worth it if 
things get screwed up or if the account gets removed because it is 
outside the ISP's acceptable use policy.

Joe


Jim wrote:
> Basically a client is currently using ISPA and having some problems so
> they want me at my ISPB to host their site from mysubdomain.domain.com.
> 
> Basically instead of moving the clients domain to ISPB I want to host a
> domain from a subdomain of mine to try to save money.
> 
> That way I am only paying for one hosting cost of domain.com but in
> reality I there is clientdomain.com which in reality is at
> mysubdomain.domain.com 
> 
> I guess since I would have to move the DNS record to ISPB then they
> might as well just host it completely but I was trying to see if I could
> host an additional domain on mysubdomain 
> 
> Jim