While 100GB is not the largest SP DB around, it clearly indicates that your organization is a regular user of the SharePoint. To that end, I would recommend a few things:
Start with splitting out SQL to a dedicated server. The reasons are numerous but include
- Scalability - the SQL Box can be scaled both in RAM and Disk easily
- Performance. Both SQL and SharePoint devour CPU cycles and RAM. By
sharing the same resources, both are slowed.
- about a hundred other reasons from Disaster Recovery to backups...
Create 1-3 Virtual Machines for SharePoint, consisting ideally of 2 load balanced Web Front Ends and 1 app server. Virtuals are relatively cheap but do not shortchange them on CPU or RAM.
This approach will allow your SharePoint farm to grow as the usage of it does - not only for your current site but for any future sites as well (i.e. Intranet Publishing, Training sites, etc..) There's a lot in 2010 that you might want to consider leveraging.
One last point, when installing your SP2010 environment, be sure to use a SQL Alias instead of referring directly to the SQL DB Machine\Instance name. This allows for greater flexibility down the road should you need to move the databases to another server.