If you need to access a guest which gets different IP due to use of DHCP, I suggest accessing via it's hostname. However accessing via hostname when the host is Windows might require an extra tool.
The following text was copied from my own answer at superuser.com.:
I suggest you use Multicast DNS to fix this.
Ubuntu is using this by default via Avahi.
The Windows host needs an Avahi-client for it to discover other Avahi-services. If your host already uses some Apple software this is probably already there via a service called Bonjour. However, if this is not already installed then a small version of Bonjour is available for download here: Bonjour Print Services. After installation you should be able to access your guest via .local.
Note: The mDNS system seem to use the .local postfix by default. So, if your hostname is "dev.myapp.com", then the actual hostname will be "dev.myapp.com.local".