Ubuntu SMB migration

[madanabhat27 at gmail.com]

Hi folks !
Our company is planning to migrate four of our PC's from an MS Windows 98/ XP/Vista environment to an Ubuntu 8.10/9.04 Environment and they have chosen me to coordinate and manage the migration and we 8-10 Personal Computers. The following are the configs of the four of them 
PC # 1 
Intel Pentium III 120MB SDRAM 40GB HDD, CD/DVD writer, MS Windows XP Home 
PC # 2
AMD Sempron, 128MB DDR2 RAM, 40GB HDD, CD writer/DVD ROM, MS Windows XP 
PC # 3 
Intel Pentium II ( Planning to upgrade to PIII ( if it is possible )  ) 64MB SDRAM ( Planning to upgrade to 256MB SDRAM  ) 24GB HDD, CD ROM, MS Windows 98 
PC # 4 
Intel Core2Duo 1.66 GHz, 2GB DDR2 RAM 160GB HDD, DVD/CD RW  MS Windows Vista Business, Intel Pro/Wireless 3945 A/B/G 
and I'd like to know, 
1.  What all are the precautionary steps I should take while migrating to ensure a safe and successful migration and?
2. What are the things I should make note of that might play an important role in the migration and?
3. Are there any good migration guides available that might help me during the migration?  and
4. Are there any good reference books that I should purchase that might help me in administering and handling those Ubuntu PC's?  and 
5. What all hardware upgrades should I do to those systems to make them Ubuntu compatible and Ubuntu ready?
6. What are all the problems I might face before,  during and after the migration?

Any help would be most appreciated

Yours,
KMB
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