Microsoft Dynamics CRM integration SharePoint

CRM <-> SharePoint integration is very common. The MS CRM blog is a good place to start for pointers:

MS CRM Blog post tagged with SharePoint

Also, the Dynamics CRM Virtual PC demo image has some SharePoint integration in it, where it shows pages from SharePoint in CRM. You can download the VPC from here:

Microsoft Dynamics CRM 4.0 Virtual Machine

Once you have the VPC started, as I recall there is SharePoint integration on the Account entity - have a look in the onload event of the Account form in Customizations.

Regarding your question in how to utilize IFrame to display custom .ASPX solution, you can refer to these posts :

Microsoft Dynamics CRM IFRAME Magic

Hope this helps